Re: about MTA's 4xx response code
On 29.08.19 10:36, Eliza wrote: I know postfix returns 4xx Response Code for Temporarily Deferred, as below: - The following addresses had fatal errors - [Status: Error, Address: , ResponseCode 421, 4.7.0 Temporarily Deferred] Message will be retried for 4 more day(s) this happens when there is some temporary reason why the mail can't be accepted/delivered. Exampes are system maintenance, disk full etc I don't like every MTA returns this 4xx code, that would make the incoming messages delay a lot time. How do you think of this? should RFC reconsider to disable 4xx code? do you want everyone to drop or reject mail just because of some temporary problems? -- Matus UHLAR - fantomas, uh...@fantomas.sk ; http://www.fantomas.sk/ Warning: I wish NOT to receive e-mail advertising to this address. Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu. Quantum mechanics: The dreams stuff is made of.
Re: about MTA's 4xx response code
on 2019/8/29 16:50, @lbutlr wrote: Only if you were very careful monitor your system for the many many corporate sanders where greylist was the effective equivalent of a blacklist (those that did not retry in violation of RFCs and this that had many servers and would resend from different ones). I tried it, but had far too many banks (refuse to resend at all) and mailers like google (many servers, never the same one twice within the greylist window) that I fairly quickly decided it wasn’t tenable. Some open lists refuse to resend then those messages are discarded. I once had a mail.ru account which have greylist policy thus open mailing lists refuse to talk to it. regards. wesley
Re: about MTA's 4xx response code
On 28 Aug 2019, at 21:06, Doug Hardie wrote: > Greylisting used to be a very effective approach to spam blocking. Only if you were very careful monitor your system for the many many corporate sanders where greylist was the effective equivalent of a blacklist (those that did not retry in violation of RFCs and this that had many servers and would resend from different ones). I tried it, but had far too many banks (refuse to resend at all) and mailers like google (many servers, never the same one twice within the greylist window) that I fairly quickly decided it wasn’t tenable. -- Because you can't cotton to evil. No Sir. You have to smack evil on the nose with the rolled-up newspaper of justice and say, 'Bad evil. Bad BAD evil”'
Re: about MTA's 4xx response code
on 2019/8/29 11:30, Bill Cole wrote: Which is their absolute right to do for whatever reason they see fit. It is NOT "abuse" in any sense. Andrew didn't mention the enhanced status codes of RFC3463, which include the '4.7.0' you are seeing in error messages. That is a generic, intentionally vague, and perfectly valid status code. Thinking the IM (like whatsapp), user send a message, the peer always says: system temporary error, please try again. That would be a terrible user experience. So as the email system. :) Just my thought. regards.
Re: about MTA's 4xx response code
On 28 Aug 2019, at 22:50, Eliza wrote: Hello, on 2019/8/29 10:42, Andrew Bernard wrote: 421 Temporary System Problem. Try again later. 421 Try again later, closing connection. 421 Server busy, try again later. The SMTP error 421 is normally used for temporary problems on the mail server or a problem with the recipients email account. Some mail providers might also return 421 after you reached a limit (restriction) on your mail account (see SMTP Error 451 below). But I know some antispam systems get abused to return 4xx even there is neither temporary system problem nor server busy. They just doubt this is suspicious message and return 4xx codes. Which is their absolute right to do for whatever reason they see fit. It is NOT "abuse" in any sense. Andrew didn't mention the enhanced status codes of RFC3463, which include the '4.7.0' you are seeing in error messages. That is a generic, intentionally vague, and perfectly valid status code. -- Bill Cole b...@scconsult.com or billc...@apache.org (AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Re: about MTA's 4xx response code
> On 28 August 2019, at 19:50, Eliza wrote: > > Hello, > > on 2019/8/29 10:42, Andrew Bernard wrote: >> 421 Temporary System Problem. Try again later. >> 421 Try again later, closing connection. >> 421 Server busy, try again later. >> The SMTP error 421 is normally used for temporary problems on the mail >> server or a problem with the recipients email account. >> Some mail providers might also return 421 after you reached a limit >> (restriction) on your mail account (see SMTP Error 451 below). > > But I know some antispam systems get abused to return 4xx even there is > neither temporary system problem nor server busy. They just doubt this is > suspicious message and return 4xx codes. Greylisting used to be a very effective approach to spam blocking. When I first implemented it a number of years ago, it blocked about 95% of the incoming mail. I believe the number of false positives was under 10. However, greylisting was based on the high cost of queueing (disk space and internet bandwidth). When the cost of those fell, spammers were able to implement queueing at very little cost. As a result greylisting became fairly ineffective. It was blocking less than 5% of the spam when I discontinued it. I suspect that most of us who implemented greylisting considered the receipt of spam to be a system problem and hence the 400 series codes were appropriate. YMMV. -- Doug
Re: about MTA's 4xx response code
Hello, on 2019/8/29 10:42, Andrew Bernard wrote: 421 Temporary System Problem. Try again later. 421 Try again later, closing connection. 421 Server busy, try again later. The SMTP error 421 is normally used for temporary problems on the mail server or a problem with the recipients email account. Some mail providers might also return 421 after you reached a limit (restriction) on your mail account (see SMTP Error 451 below). But I know some antispam systems get abused to return 4xx even there is neither temporary system problem nor server busy. They just doubt this is suspicious message and return 4xx codes. regards.
Re: about MTA's 4xx response code
Hi, Here's an extract from a site about 421: SMTP Error 421 421 Temporary System Problem. Try again later. 421 Try again later, closing connection. 421 Server busy, try again later. The SMTP error 421 is normally used for temporary problems on the mail server or a problem with the recipients email account. Some mail providers might also return 421 after you reached a limit (restriction) on your mail account (see SMTP Error 451 below). Does this help? Suggesting the RFC be modified is off the table, because that is not the problem. RFC's are very seriously thought out and hugely important documents, tested and approved by serious committees. Looking. Sure, they get updated, but not for reasons related to issues like this. Andrew On 29/8/19 12:36 pm, Eliza wrote: I know postfix returns 4xx Response Code for Temporarily Deferred, as below: - The following addresses had fatal errors - [Status: Error, Address: , ResponseCode 421, 4.7.0 Temporarily Deferred] Message will be retried for 4 more day(s) I don't like every MTA returns this 4xx code, that would make the incoming messages delay a lot time. How do you think of this? should RFC reconsider to disable 4xx code?
