Andrew McGlashan wrote:
On 15/02/2012 7:20 PM, Matthew Cengia wrote:
On 2012-02-15 19:03, Jason White wrote: [...]
based on a few minutes of reading, I couldn't find anything in RFC2821 that would require it.
FYI, this is obsoleted by RFC5321 now (and updated by 5336).
Okay, well it doesn't appear to be part of the standards, but it is painful for greylisting. Although I can understand that one IP may become blocked or have issues, whilst an alternate (sending) IP might be fine.
When you run into such a site, it is a good idea to (attempt to) notify the site's sysadmin that he is, indirectly, making life easier for spammers.
After all, there's a slight chance that 1) they don't know there's a problem; 2) they're technically comptetent enough to fix it; and 3) enough sysadmins complain that they're actually motivated to do so.
Ah, who am I kidding...
Aside from the previously mentioned "retry from a different IP" that used to mess with my greylists, every problem reported to me about my spam filter has been caused by an RFC violation, which places me in the unfortunate position of being stuck between a rock and a hard place. The only one i'm inclined to give some wiggle room on is where the envelope recipient is valid, but a cc in the mail header is invalid (often just badly formatted "undisclosed recipient" text). Exim header validation is (or was... maybe I'm a bit behind) all-in or none-in, but even those I've been able to get the sender to fix up, except where mailing lists are involved. James