Dan Slay wrote:
Thanks, that's what I have read. Which is why this make things more awkward.
I cannot see that holding a recipient list is a solution. If, for
instance, you relay for thousands of domains all going to different
MTA's that hold each individual domains recipient list, its not really
that straight forward and may impact performance?
Postfix can generate and maintain an internal recipient list by means of
a recipient check on the downstream MTA before accepting mail to a
previously unknown user. See these pages for information on how it works:
http://www.postfix.org/postconf.5.html#reject_unverified_recipient
http://www.postfix.org/ADDRESS_VERIFICATION_README.html#recipient
Correctly configured, with the right degree of persistance in the cache,
this will have minimal impact on performance while also significantly
reducing backscatter. The actual tradeoff between effectiveness and
performance is dependent on how long data is cached for; if your system
can cope with it then it's best not to cache at all as that's the only
way to ensure zero backscatter. But even a fairly lengthy cache time
will be sufficient to prevent the majority of backscatter, provided that
the recipient email addresses don't get switched off very often.
Mark
