There is a checkbox in the Advanced Delivery dialog that reads "Perform
reverse DNS lookup on incoming messages". What is the point of this
checkbox? I was hoping it meant that the SMTP server would reject
connections where RDNS failed. But that doesn't appear to be the case. Is
there another way to block those connections?

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> What  is  the point of this checkbox? I was hoping it meant that the
> SMTP  server  would  reject  connections where RDNS failed.

Yes, we all had that hope once. 

It'll _tag_ messages that have a non-empty HELO that doesn't match the
empty  or  non-empty  PTR,  but it won't reject them at the connection
level.  To  do more than that, you'd need an event sink that does more
connection-time processing.

IMO,  it's  in  a sense good that such an easy-to-flip feature doesn't
reject  all  roundtrip  failures without any means of whitelisting. As
effective as the roundtrip test has proven to be, being able to ignore
it  for V.I.P./sloppy-yet-legit servers is essential. With tagging, at
least  you  could interpret the roundtrip failure in a post-acceptance
anti-spam  system  that itself offers whitelisting (though that system
might  do  the  lookup  itself  just  as  easily,  and post-acceptance
weighting   of  data  that  was  wholly  available  pre-acceptance  is
backward).

--Sandy

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