[Discuss] Exim sender_verify issue?

[pjalajas at tebuco.com (Peter Jalajas)]

Hi all,

I had a mildly interesting problem this week, coincidentally related to
some of the recent threads on this list.

I host websites for some friends and family(!) at a hosting provider that
has had awesome support service for many years.  This week I had a problem
where one of my hosting clients was not receiving all of the email from
their friend; the friend was sometimes receiving "550 Sender verify failed".

Looking way too deeply into it, I discovered that the _sender's_ DNS had a
couple of problems:
a) no A record (but they did have the standard several Google App MX
records), and
b) one of their 3 nameservers was dead.

But that revealed what I think are a couple of problems on _my_ server.
My Exim server, for sender_verify:
a) was only checking for A records, not MX records; and/or
b) was not checking multiple nameservers.

(I'm guessing Exim was also not _retrying_ any nameservers, but that's
off-topic for the moment.)

(To be clear, we are _not_ doing callouts/callbacks.)

My hosting provider has been awesome over many years, but I'm not getting
satisfaction on this issue, even after escalating up to Level II.  But
maybe it's me.  What do you think?  Is that just how Exim and/or
sender_verify (and other mail servers) behave, as my hosting support folks
are implying?

Thanks,
Pete