Zitat von Graham Murray <graham(_at_)gmurray(_dot_)org(_dot_)uk>:
Meng Weng Wong <mengwong(_at_)dumbo(_dot_)pobox(_dot_)com> writes:
hence greylisting, and accreditation and reputation systems.
And greylisting can be a problem as well. There are some broken mail
systems (sending legitimate mail) which treat the greylister's
"temporary failure, please try later" as a delivery acceptance and
never resend. Nor do they (or the particular one I have encountered)
give a non-delivery report to the sender.
If the sender is not able to speak SMTP or follow the RFC there is nearly
nothing you can do.
Greylisting has other problems with farms of random sending servers, one time
sender addresses and the like though. That said it is the best weapon against
random mail sending trojaned zombie machines.
Regards
Andreas