RE: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
> I haven't seen any succinct justification for providing a > 550 message rejection for positively-identified spam versus > silently dropping the message. Lots of how-to instructions > but no whys. > > matthew black > california state university, long beach Because your father may forward a copy of a Nigeria scam from a new email address he just got with his new ISP and ask if you if he should send them money. Because a machine you own may be responsible for the spam, and someone may be forwarding you a copy of it along with the tracking information to demonstrate that you were responsible for it. Because the spam may include a trademark you own and you may need to notify your legal department about it. The spam may have been helpfully forwarded to you by someone familiar with your trademarks. Because if you say you are going to deliver a message, that's what you should do. Because being spam is not the same as being unimportant. All of these things really do happen. >Agreed, but we're willing to live with an error rate of less >than one in a million. This isn't a space shuttle. I don't think >the USPS can claim 99.% delivery accuracy. Nonetheless, to >allay worries, we are considering spam quarantines to allow >recipients an opportunity to review spam messages themselves, much >like Yahoo! Mail. It is one thing to have an error rate of one in a million, it is quite another thing to choose to have an error rate of one in a million instead of one in a billion for no rational reason at all. If the measure is what fraction of positively-identified spam the recipient would probably rather receive than not receive, it's probably more like one in 5,000. If the measure is what fraction of positively-identified spam the recipient would rather the sender get a reject than silently discard, it's probably more like one on 20,000. The argument on the other side is if the positively-identified spam comes from a business-critical mailing list that unsubscribes people if they have too many bounces. This probably isn't an issue for viruses and malware because these rarely get past the filters these lists already have. It is a big issue for spam and one of the few for which there is no good solution I know of. (Other than having the recipient whitelist the list at the MTA, which is hard to do.) DS
Re: Spam filtering bcps
On Wed, Apr 12, 2006 at 03:35:51PM -0400, [EMAIL PROTECTED] wrote: > On Wed, 12 Apr 2006 14:28:59 CDT, Bryan Bradsby said: > > > > > Silently deleting other people's e-mail should never even be considered. > > > > Unless that email is a virus, or a spam with a forged envelope sender. > > No, in that case you 550 the sucker. Unfortunately there is plenty of mailing list manager software that will disable your subscription if your mail is rejected enough times. Mailman being a good example. I have been unsubbed from mailman lists that have allowed viruses through, even with the default mailman settings for boucne processing. In a perfect world, no mailing lists distribute spam, viruses and malware. At the moment therefore while practicing reject after DATA I do find it necessary to mark as spam and accept if it has Precedence: bulk (or list or whatever), because otherwise my users complain and "don't subscribe to poorly-managed lists then" is not an acceptable answer for them. Regards, Andy signature.asc Description: Digital signature
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
On Wed, 12 Apr 2006 18:56:44 -0700 (PDT) "Steve Thomas" <[EMAIL PROTECTED]> wrote: How does one properly report delivery failure to a guerrilla spammer? If you accept the message, you can presumably deliver it. In this day and age, anyone accepting mail for a domain without first checking the RCPT TO - even (especially?) on a backup MX - should have their head examined. In the event that the RCPT TO is valid but the message truly can't be delivered for some other reason, In this day and age it is not always possible to check for valid addresses at a border SMTP gateway. Sites have multiple legacy systems which are not very interoperable. Some e-mail gateways are incapable of scanning messages in-line. How does that make the gateway junk or the system administrator an idiot or incompetent? you should bounce the message and fix the problem. This is advocating collateral damage because nearly all spam and viruses have return paths which falsely implicate innocent victims (i.e., blowback). Users don't want it delivered or dropped in their junk folder; most wouldn't know what to do with a junk folder. E-mail systems require investments in the 100s of thousands of dollars, not some Windows PC running Linux. The largest part of the cost equation is personnel and training, not hardware. Large organizations like our shy away from open source software in many situations NOT because it's open source. We opt for commercial solutions so employees, like me, can take vacation and know that other employees can handle problems and let me enjoy my vacation without carrying a pager (unless you think it's cool to be tethered to your job 24/7 with a Blackberry). Dogmatic adherence to a literal reading of every RFC is impractical. When my organization decided to drop BrightMail postively-identified spam, we accepted a FP rate of less than one in a million as a good thing, fully aware that this violated RFC 821. I used to love sendmail but recommended our organization drop it. Sendmail's queue processing algorithm was (is?) hopelessly broken and delayed e-mail for hours or just discarded it after five days because sendmail couldn't properly prioritize the queue. With our IronPort C60 gateway, almost all e-mail is processed sub-second, users don't see postiviely-identified spam, and viruses and phishing attempts are a thing of the past. Should I no longer be able to perform my duties, for whatever reason, our e-mail system will continue running and someone else can take on my responsibilities with a tiny learning curve. No worries about whether SpamAssassin got it's update. No worries about whether ClamAV will be running next month. No worries about system outages during complicated open-source software upgrades, even for a few minutes. Unless you feel those are OK. Ask yourself this question: can your organization survive a loss of its entire technical staff? Would new employees be able to manage your systems or would chaos result? matthew black california state university, long beach
SMTP: run-to-completion, backscatter, et cetera (Re: Spam filtering bcps ...)
ST> Date: Wed, 12 Apr 2006 18:56:44 -0700 (PDT)
ST> From: Steve Thomas
ST> If you accept the message, you can presumably deliver it. In this
Possibly. However, insufficient storage is not the only cause of 4xx
status.
ST> day and age, anyone accepting mail for a domain without first
ST> checking the RCPT TO - even (especially?) on a backup MX - should
ST> have their head examined.
Especially.
ST> IN the event that the RCPT TO is valid but the message truly can't
ST> be delivered for some other reason, you should bounce the message
ST> and fix the problem.
*Iff* the bounce can be sent to the correct location. That's a big
iff these days.
ST> My point was that when it comes to spam, it should either be rejected
ST> inline or delivered.
That's ideal. I can think of several realistic conditions where a
message could be queued but not validated until later. I'm simply
stating that { accepted | pending | refused } is a reasonable set of
responses. From an end-to-end perspective, SMTP transactions are
asynchronous and not guaranteed, anyway.
You're advocating run-to-completion. I'm suggesting an asynchronous
realtime system instead. Polls could be coalesced.
Note also the implications of polling for message status: Eliminate
bounces. Want to know if a message went through? Poll. Receive bounce
inline if appropriate. That seems better than the current push-based
crapshoot.
Want to confirm that a user has retrieved a message? Now possible at
the MX level. Want to confirm receipt by the server without divulging
if the user has retrieved the message? Return a status code indicating
such.
Frankly, I'd go for pull-based response codes just to be rid of
backscatter. The rest is gravy.
Eddy
--
Everquick Internet - http://www.everquick.net/
A division of Brotsman & Dreger, Inc. - http://www.brotsman.com/
Bandwidth, consulting, e-commerce, hosting, and network building
Phone: +1 785 865 5885 Lawrence and [inter]national
Phone: +1 316 794 8922 Wichita
DO NOT send mail to the following addresses:
[EMAIL PROTECTED] -*- [EMAIL PROTECTED] -*- [EMAIL PROTECTED]
Sending mail to spambait addresses is a great way to get blocked.
Ditto for broken OOO autoresponders and foolish AV software backscatter.
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
> How does one properly report delivery failure to a guerrilla spammer? If you accept the message, you can presumably deliver it. In this day and age, anyone accepting mail for a domain without first checking the RCPT TO - even (especially?) on a backup MX - should have their head examined. In the event that the RCPT TO is valid but the message truly can't be delivered for some other reason, you should bounce the message and fix the problem. My point was that when it comes to spam, it should either be rejected inline or delivered. Unless your spam scanner has 100% accuracy, 100% of the time, there is no justification for sending anything not addressed to you to /dev/null. > "Please automatically delete anything that might be spam. They'll call > me if it's important. I know I'll lose some mail, but that's okay." If you have an agreement with a customer that specifically allows for such behaviour, great. We can get into individual cases for any concievable scenario, but that would be silly. It was pretty clear, to me at least, that we were discussing this as it would pertain to a system-wide configuration. > As for MUST bounce using return-path... perhaps you've never experienced > blowback from a joe job. It can be unpleasant. Yes, I have. And yes, it is. However, I never suggested bouncing spam, as my last message clearly stated. My position is that if you accept the message (250 OK), you have an obligation to deliver it. If you can't scan it during the SMTP transaction, do it after and mark up the headers, drop it in a junk folder - whatever - but don't delete it. St-
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
ST> Date: Wed, 12 Apr 2006 10:16:53 -0700 (PDT) ST> From: Steve Thomas ST> RFC 2821? ST> ST> ...the protocol requires that a server accept responsibility ST> for either delivering a message or properly reporting the ST> failure to do so. How does one properly report delivery failure to a guerrilla spammer? ST> Unless you're the final recipient of the message, you have no business ST> deleting it. If you've accept a message, you should either deliver or ST> bounce it, per RFC requirements. "Please automatically delete anything that might be spam. They'll call me if it's important. I know I'll lose some mail, but that's okay." Throwing RFC 2821 at that user probably would not have made them happy. As for MUST bounce using return-path... perhaps you've never experienced blowback from a joe job. It can be unpleasant. RFCs are for maintaining interoperability. They are not infallible. When a system is clearly broken, it's time to examine alternatives -- not to say that the RFC was handed down from on high. Proposal: MXes can say "2xx message queued with ID blahblahblah". They also can return 4xx "try back later codes". Yes? How about some return code that says "poll by $deadline if you want to know whether message ID blahblahblah was accepted or rejected"? No need to retransmit the entire message, and the sender can learn whether the message was actually accepted. Eddy -- Everquick Internet - http://www.everquick.net/ A division of Brotsman & Dreger, Inc. - http://www.brotsman.com/ Bandwidth, consulting, e-commerce, hosting, and network building Phone: +1 785 865 5885 Lawrence and [inter]national Phone: +1 316 794 8922 Wichita DO NOT send mail to the following addresses: [EMAIL PROTECTED] -*- [EMAIL PROTECTED] -*- [EMAIL PROTECTED] Sending mail to spambait addresses is a great way to get blocked. Ditto for broken OOO autoresponders and foolish AV software backscatter.
Re: Spam filtering bcps
Bryan Bradsby wrote: Silently deleting other people's e-mail should never even be considered. Unless that email is a virus, or a spam with a forged envelope sender. Why? - You can scan for viruses inline using a variety of products (eg: I have patched Postfix to use clamav inline on modest hardware (single CPU AMD64 will do it, so will a Dual PIII 866) and it will accept messages at 50 messages per second (sustained load) and scan for viruses before responding to the end-of-data command, rejecting if a virus is detected.). Spam is a different subject altogether - are you that sure you can detect spam without a false positive? If so then why aren't you doing it inline? If you can't why are you blindly deleting the messages? - My BCP comment is if you can't detect inline (eg for performance reasons) tag it and deliver it (if you have the capabilities, deliver it to a junk folder) - that way you are following the RFC's and no non spam mail is deleted by the system. Regards, Mat
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
Steve Thomas wrote: Earlier today, I said: Unless you're the final recipient of the message, you have no business deleting it. If you've accept a message, you should either deliver or bounce it, per RFC requirements. I just want to clarify that I was in no way suggesting that anyone bounce spam - I was merely pointing out that if you choose to 250 a message, you have to deliver it. The much better option is to 550 it after DATA if you don't like what you see. Silently deleting other people's e-mail should never even be considered. This policy I whole heartedly agree with, and I strive where ever possible to enforce this in every place I work, where ever people get listed in SORBS for backscatter, I work with them telling them how they can do this With the current technologies available there is no reason a small-medium organisation cannot virus and spam scan mail inline at the SMTP transaction stage. (Even the barracuda's can spamassassin scan at around 8 messages per second - my previous employment were receiving around 4 messages per second - which translated to 1-2 million emails per day) It is possible to do inline scanning in larger ISPs (I personally have configured a 'system' to handle upto 90 message per second inline scanning) - though it requires a lot more planning, thought, and careful consideration. Regards, Mat
Re: Spam filtering bcps
On Wed, 12 Apr 2006 14:28:59 -0500 (CDT) Bryan Bradsby <[EMAIL PROTECTED]> wrote: Silently deleting other people's e-mail should never even be considered. Unless that email is a virus, or a spam with a forged envelope sender. -bryan bradsby Aha, so there are situtations where this is acceptable? What about deleting viral attachments or altering subject lines...is that permissible? The sweeping generalizations I've read leave little room for responding to real-world situations. matthew black california state university, long beach
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
On Wed, 12 Apr 2006 14:18:24 -0400 [EMAIL PROTECTED] wrote: On Wed, 12 Apr 2006 10:16:53 PDT, Steve Thomas said: > I haven't seen any succinct justification for providing a > 550 message rejection for positively-identified spam versus > silently dropping the message. Lots of how-to instructions > but no whys. RFC 2821? ...the protocol requires that a server accept responsibility for either delivering a message or properly reporting the failure to do so. Your statement is open to multiple interpretations. I argue that anytime our system identifies a message as spam that it gets delivered to the system bit bucket. RFC-821 and netiquette also "mandate" e-mail be properly addressed. System manufacturers and administrators make compromises because strict adherence to the rules is not always possible from an operational perspective. Elsewhere in 2821 (6.1, to be specific): When the receiver-SMTP accepts a piece of mail (by sending a "250 OK" message in response to DATA), it is accepting responsibility for delivering or relaying the message. It must take this responsibility seriously. It MUST NOT lose the message for frivolous reasons, such as because the host later crashes or because of a predictable resource shortage. Lost me on that part about crashes being frivolous reasons. This is a political statement not an indisputable matter of fact. OK? Got that? You '250 OK' it, you got a *serious* responsibility. Losing the message because the whole damned machine crashes is considered a frivolous reason. And throwing it away because you don't like the way it looks is OK? Man, ...*** you're in for some severe karmic protocol payback down the road... ;) I'm not the one throwing them away and never look at them; watch the finger wagging. And thanks for the karma heads up, Bhudda. matthew black california state university, long beach
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
On Wed, Apr 12, 2006 at 12:03:51PM -0400, Joe Maimon wrote: > Matthew Black wrote: > > > there's no bandwidth savings from silently dropping the message > > versus providing a 550 rejection. In the best of all worlds, > > it would be nice to give feedback. No system is perfect and a > > false-positive rate of less than one in a million "220" accepted > > messages seems pretty small. > > Let me ask you this simple question: > > If you know at close of DATA whether you are going to actually perform > final delivery, what does it cost you to follow standards and issue a > 550 instead of a 220 and discard it? > > If you use a 550, a real live person sending an email that somehow gets > FP will actually benefit. In today's world, at least with the spamtorrent I see at my clients, that's just untrue. If your filtering is set up well, and you mark an e-mail as SPAM, it almost certainly is (yes, I'll certainly concede FP's exist, but again, it almost certainly doesn't matter that much in that teensy number of occurrences); and 99-plus-percent of spam is emitted from spambots who don't give a $expletive about return status one way or another. If you're worrying about "no-status" in the context of FP's, then your filtering isn't set up well, which really means you've got larger problems. > I am with Suresh on this, just like in the past threads. Search the archive. Though not contradicting what I just wrote, so am I. However, header-forged and multi-chained spam from firehose-like spambots don't play by any of our rules; all they do is blast away in a largely one-way transaction (guess which direction!). A 550 now-a-days has nowhere to "go" (and those "commercial" akak "legit") spamhouses don't wash their lists even on 550's. -- Henry Yen Aegis Information Systems, Inc. Senior Systems Programmer Hicksville, New York
Re: Spam filtering bcps
On Wed, 12 Apr 2006 14:28:59 CDT, Bryan Bradsby said: > > > Silently deleting other people's e-mail should never even be considered. > > Unless that email is a virus, or a spam with a forged envelope sender. No, in that case you 550 the sucker. pgpOxV2xehNAo.pgp Description: PGP signature
Re: Spam filtering bcps
> Silently deleting other people's e-mail should never even be considered. Unless that email is a virus, or a spam with a forged envelope sender. -bryan bradsby
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
Earlier today, I said: > Unless you're the final recipient of the message, you have no business > deleting it. If you've accept a message, you should either deliver or > bounce it, per RFC requirements. I just want to clarify that I was in no way suggesting that anyone bounce spam - I was merely pointing out that if you choose to 250 a message, you have to deliver it. The much better option is to 550 it after DATA if you don't like what you see. Silently deleting other people's e-mail should never even be considered. Returning to lurk status... St-
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
On Wed, 12 Apr 2006 10:16:53 PDT, Steve Thomas said: > > > I haven't seen any succinct justification for providing a > > 550 message rejection for positively-identified spam versus > > silently dropping the message. Lots of how-to instructions > > but no whys. > > RFC 2821? > > ...the protocol requires that a server accept responsibility > for either delivering a message or properly reporting the > failure to do so. Elsewhere in 2821 (6.1, to be specific): When the receiver-SMTP accepts a piece of mail (by sending a "250 OK" message in response to DATA), it is accepting responsibility for delivering or relaying the message. It must take this responsibility seriously. It MUST NOT lose the message for frivolous reasons, such as because the host later crashes or because of a predictable resource shortage. OK? Got that? You '250 OK' it, you got a *serious* responsibility. Losing the message because the whole damned machine crashes is considered a frivolous reason. And throwing it away because you don't like the way it looks is OK? Man, you're in for some severe karmic protocol payback down the road... ;) pgpmW5ds5R1xP.pgp Description: PGP signature
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
> I haven't seen any succinct justification for providing a > 550 message rejection for positively-identified spam versus > silently dropping the message. Lots of how-to instructions > but no whys. RFC 2821? ...the protocol requires that a server accept responsibility for either delivering a message or properly reporting the failure to do so. ... If an SMTP server has accepted the task of relaying the mail and later finds that the destination is incorrect or that the mail cannot be delivered for some other reason, then it MUST construct an "undeliverable mail" notification message and send it to the originator of the undeliverable mail (as indicated by the reverse-path). Unless you're the final recipient of the message, you have no business deleting it. If you've accept a message, you should either deliver or bounce it, per RFC requirements.
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
Matthew Black wrote: there's no bandwidth savings from silently dropping the message versus providing a 550 rejection. In the best of all worlds, it would be nice to give feedback. No system is perfect and a false-positive rate of less than one in a million "220" accepted messages seems pretty small. I thought I had already participated in beating this dead horse sufficiently in multiple threads in multiple forums on multiple occasions. Maybe I am in your killfile or something. If I post again on this topic, I certainly will deserve to be. Let me ask you this simple question: If you know at close of DATA whether you are going to actually perform final delivery, what does it cost you to follow standards and issue a 550 instead of a 220 and discard it? If you use a 550, a real live person sending an email that somehow gets FP will actually benefit. I am with Suresh on this, just like in the past threads. Search the archive.
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
On Wed, 12 Apr 2006 21:12:44 +0530 "Suresh Ramasubramanian" <[EMAIL PROTECTED]> wrote: On 4/12/06, Matthew Black <[EMAIL PROTECTED]> wrote: Where is the bandwidth savings once we've accepted an entire message, scanned it, determined it was spam, then provided a 550 rejection versus silently droping? If you can scan it inline, you can stop, issue a 550 and drop the SMTP connection any time you want. Like for example, midstream when you discover a fake header pattern. You'd start with whatever can be rejected in session - fake HELOs, blocklist listed IPs, random faked headers, dodgy attachment types that are more likely to be viruses than not Then apply the heavier and more cpu intensive filters later, on a much smaller volume of spam We already do this. Maybe not all that much of a bandwidth / cpu saving, but saving remote postmasters the hassle of troubleshooting lost email is always a good idea. After all said methods have been performed and the message gets through reputation filtering; blacklists; forged/munged headers, e-mail addresses, domain names the message comes in and then there's that final dot. Up to this point, the message hasn't proven to be spam until it can be scanned using BrightMail, SpamAssassin, Baysian filters, DCC lists, or other methods. All I'm saying is that once the full DATA submission has completed, there's no bandwidth savings from silently dropping the message versus providing a 550 rejection. In the best of all worlds, it would be nice to give feedback. No system is perfect and a false-positive rate of less than one in a million "220" accepted messages seems pretty small. matthew black california state university, long beach
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
On 4/12/06, Matthew Black <[EMAIL PROTECTED]> wrote: > Agreed, but we're willing to live with an error rate of less > than one in a million. This isn't a space shuttle. I don't think > the USPS can claim 99.% delivery accuracy. Nonetheless, to I'm not even saying five nines. Spam filtering - even with heuristics etc - is less than perfect, and per user spam filtering, however idiot proof, sometimes turns out to be like giving Acme Inc gadgets to Wile E Coyote. [users having fun with procmail and .forwards should already be a familiar story I guess?] > We already reject most connections with a 550 or TCP REFUSE > based on reputation filtering and blacklists, et al. That works just fine. I dont have any argument with it > Where is the bandwidth savings once we've accepted an entire message, > scanned it, determined it was spam, then provided a 550 rejection > versus silently droping? If you can scan it inline, you can stop, issue a 550 and drop the SMTP connection any time you want. Like for example, midstream when you discover a fake header pattern. You'd start with whatever can be rejected in session - fake HELOs, blocklist listed IPs, random faked headers, dodgy attachment types that are more likely to be viruses than not Then apply the heavier and more cpu intensive filters later, on a much smaller volume of spam Maybe not all that much of a bandwidth / cpu saving, but saving remote postmasters the hassle of troubleshooting lost email is always a good idea. -- Suresh Ramasubramanian ([EMAIL PROTECTED])
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
On Wed, 12 Apr 2006 20:30:16 +0530 "Suresh Ramasubramanian" <[EMAIL PROTECTED]> wrote: On 4/12/06, Matthew Black <[EMAIL PROTECTED]> wrote: I haven't seen any succinct justification for providing a 550 message rejection for positively-identified spam versus silently dropping the message. Lots of how-to instructions but no whys. For viruses - fine. But you are not going to find any spam filter in the world that doesnt have false positives. And in such cases its always a good idea to let the sender know his email didnt get through. Agreed, but we're willing to live with an error rate of less than one in a million. This isn't a space shuttle. I don't think the USPS can claim 99.% delivery accuracy. Nonetheless, to allay worries, we are considering spam quarantines to allow recipients an opportunity to review spam messages themselves, much like Yahoo! Mail. Complaints about e-mail not getting through won't be solved with a 550 versus silently dropping spam because most users aren't willing to sift through e-mail errors to find the specific cause for delivery failure. Members of this list are a rare exception. Like for example - you see a large webmail provider whose hosts and domains keep getting forged into spam, misread the headers and block that provider. In such cases, its your users who arent getting a lot of valid email from their friends and relatives who are using that provider, and 550'ing instead of trashing email saves the senders, and their provider, quite lot of time that'd otherwise be spent troubleshooting the issue. Plus, 5xx smtp rejects tend to save your bandwidth a bit compared to accepting the entire email (not that it matters on a small university domain where your userbase is going to be fairly small, and bandwidth available quite generous .. but for larger sites, or sites with bandwidth issues, that's definitely a concern) We already reject most connections with a 550 or TCP REFUSE based on reputation filtering and blacklists, et al. Where is the bandwidth savings once we've accepted an entire message, scanned it, determined it was spam, then provided a 550 rejection versus silently droping? matthew black california state university, long beach
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
On Wed, 12 Apr 2006, Matthew Black wrote: > > I haven't seen any succinct justification for providing a > 550 message rejection for positively-identified spam versus > silently dropping the message. If you are wrong about the message being spam, then the sender gets a bounce. Tony. -- f.a.n.finch <[EMAIL PROTECTED]> http://dotat.at/ BERWICK ON TWEED TO WHITBY: WEST OR SOUTHWEST 5 OR 6, PERHAPS INCREASING 7 LATER IN NORTH. RAIN AT FIRST. MAINLY GOOD. SLIGHT OR MODERATE.
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
On 4/12/06, Matthew Black <[EMAIL PROTECTED]> wrote: > > I haven't seen any succinct justification for providing a > 550 message rejection for positively-identified spam versus > silently dropping the message. Lots of how-to instructions > but no whys. > For viruses - fine. But you are not going to find any spam filter in the world that doesnt have false positives. And in such cases its always a good idea to let the sender know his email didnt get through. Like for example - you see a large webmail provider whose hosts and domains keep getting forged into spam, misread the headers and block that provider. In such cases, its your users who arent getting a lot of valid email from their friends and relatives who are using that provider, and 550'ing instead of trashing email saves the senders, and their provider, quite lot of time that'd otherwise be spent troubleshooting the issue. Plus, 5xx smtp rejects tend to save your bandwidth a bit compared to accepting the entire email (not that it matters on a small university domain where your userbase is going to be fairly small, and bandwidth available quite generous .. but for larger sites, or sites with bandwidth issues, that's definitely a concern) --srs -- Suresh Ramasubramanian ([EMAIL PROTECTED])
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
Several people kindly contacted me off list with laborious explanations of how to implement delayed 550 rejections using sedmail, et al. We gave up sendmail years ago in favor of a competing solution. I haven't seen any succinct justification for providing a 550 message rejection for positively-identified spam versus silently dropping the message. Lots of how-to instructions but no whys. matthew black california state university, long beach
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
Matthew Sullivan wrote: Suresh Ramasubramanian wrote: On 4/11/06, Matthew Black <[EMAIL PROTECTED]> wrote: Are you suggesting that we configure our e-mail servers to notify people upon automatic deletion of spam? Frequently, spam cannot be properly identified until closure of the SMTP conversation and that final 200 mMESSAGE ACCEPTED...or do you think that TCP/IP connection should be held open until the message can be scanned for spam and viruses just so we can give a 550 MESSAGE REJECTED error instead of silently dropping it? You can reject right after DATA, at the . stage, before QUIT That's still an in line smtp reject rather than an accept + bounce DSN. Exim with the spamassassin patches (sa-exim) does this, for example. -srs Of course Postfix can be setup (using spampd) with spamassassin to do exactly the same. I believe Sendmail+MimeDefang+Spamassassin will also reject inline if set to do so. Regards, Mat As will sendmail+spamass-milter+spamassassin In fact there are quite a few milters that can be used in between sendmail and spamassassin Joe
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
Suresh Ramasubramanian wrote: On 4/11/06, Matthew Black <[EMAIL PROTECTED]> wrote: Are you suggesting that we configure our e-mail servers to notify people upon automatic deletion of spam? Frequently, spam cannot be properly identified until closure of the SMTP conversation and that final 200 mMESSAGE ACCEPTED...or do you think that TCP/IP connection should be held open until the message can be scanned for spam and viruses just so we can give a 550 MESSAGE REJECTED error instead of silently dropping it? You can reject right after DATA, at the . stage, before QUIT That's still an in line smtp reject rather than an accept + bounce DSN. Exim with the spamassassin patches (sa-exim) does this, for example. -srs Of course Postfix can be setup (using spampd) with spamassassin to do exactly the same. I believe Sendmail+MimeDefang+Spamassassin will also reject inline if set to do so. Regards, Mat
Re: Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
On Wed, 12 Apr 2006, Suresh Ramasubramanian wrote: > > Exim with the spamassassin patches (sa-exim) does this, for example. SpamAssassin support is built in to Exim since version 4.50. Tony. -- f.a.n.finch <[EMAIL PROTECTED]> http://dotat.at/ BERWICK ON TWEED TO WHITBY: WEST OR SOUTHWEST 5 OR 6, PERHAPS INCREASING 7 LATER IN NORTH. RAIN AT FIRST. MAINLY GOOD. SLIGHT OR MODERATE.
Spam filtering bcps [was Re: Open Letter to D-Link about their NTP vandalism]
On 4/11/06, Matthew Black <[EMAIL PROTECTED]> wrote: > > Are you suggesting that we configure our e-mail servers to notify > people upon automatic deletion of spam? Frequently, spam cannot be > properly identified until closure of the SMTP conversation and that > final 200 mMESSAGE ACCEPTED...or do you think that TCP/IP connection > should be held open until the message can be scanned for spam and > viruses just so we can give a 550 MESSAGE REJECTED error instead of > silently dropping it? > You can reject right after DATA, at the . stage, before QUIT That's still an in line smtp reject rather than an accept + bounce DSN. Exim with the spamassassin patches (sa-exim) does this, for example. -srs
