> how does verify = sender work. I can't find anything that says what
> it does exactly in the docs. I'm seeing a valid sender get rejected
> several times before being finally accepted.
As Jeremy Harris covered, 'verify = sender' attempts to route the
sender address and uses the result. One consequence of this is that
you can manually test whether a sender address will route and why
it's failing with 'exim -bt <address>', possibly adding debug flags
as necessary to extract things like DNS failure information.
(If the DNS failure is erratic, this may not entirely help. In that
case, force-flushing or force-restarting the DNS cache of your local
resolving DNS server may help to make the problem happen.)
- cks
