Loren Wilton wrote: > > > In my logic, there is no valid reason that a remote sender would connect > > directly to our SMTP server from their dynamic/DSL/cable IP to send our > > customer's an email ... I think ? Valid 'remote to local' emails being > > sent from these DSL/cable/dialup IP would normally be relayed via their > > own network's SMTP server, which would then be delved to us by a host > > that didn't match the dynamic/DSL/cable custom rule. Right? > > > > It would either be a 'zombie' spam relay', or some one who setup a SMTP > > server on a dynamic IP (which just isn't what valid businesses do ... )? > > I think your reasoning is generally sound. I think though that it is > probably possible for someone to have a 'valid business' with a small server > (or maybe even single machine) on a DSL or the like connection. I would > hope though that it wouldn't be dynamic IP. Although I suppose it might be > if their telco has problems giving out fixed IP addresses. I'm not sure how > DNS would manage to resolve foobar.com down to them if the ip address keeps > changing though. > > My guess is that you could potentially be locking out some few mom-n-pop > businesses from your network. I think I'd balance that against locking out > the zombies and plain stupid spammers, and probably come down on the side of > doing it anyway. >
On the plus side, any legitimate service run on those addresses can _still_ send its outgoing email through the ISP's mail servers (even if they have their own local mail server, it can still be configured to send outgoing email through their ISP instead of direct to the target mail servers). So, the mom'n'pop businesses have no excuse, except maybe their own ineptitude, which is not (in my book) an acceptable excuse. They'll also have to remember to factor their ISP into their SPF plan, too. On the minus side, for the general case (which may not apply to the original poster): you might have some of your own employees set up to send their email straight from home to work (esp. if it's a laptop, where one SMTP server set up is easier for roaming than having 1 account with multiple SMTP servers based upon where the user happens to be sitting at that point in time). There are ways to dealing with those people (SMTP-AUTH, message submission port, 2nd server, VPN, etc.), but you still have to factor them into your plan if they exist in your set up. Otherwise ... you're right: there's no good reason to accept messages sent from dynamic IP address blocks. Even if they are a mom'n'pop type legit business, they can send it through their ISP's SMTP server instead of connecting directly to you.
