Moin,
Emmanuel Noobadmin <centos.admin@???> (Di 02 Feb 2016 19:56:58 CET):
…
> What happens is that email sending gets stuck at "Connecting" (when
> using Thunderbird) for a long time before delivery is made. Comparing
> exim -bd -d output on the problem server and a "normal" server, the
> problem seems to be this:
>
> The problematic exim install is doing dns lookup for every single
> recipient and does not continue until it finishes. At 5~15 sec per
> recipient, this becomes an enormous lag.
Yes, as Jeremy wrote, it's in the ACL, there probably is some
verify = recipient
This is done during SMTP time, that is, during the time your MUA is
talking to the server.
As DNS normally shouldn't take 5…15 secs per query, I'd assume that
either your DNS is broken (Exim uses the hosts resolver libraries, you
should be able to do debugging using dig & co.)
Or you're doing callouts, these may take a while, depending on how fast
the recipient host is. (verify = recipient/callout)
Normally you want to have these SMTP time recipient verification (if you
want to have callouts … hm, that's a religious issue :))
Doing as much as possible checking is good to avoid bounces. BUT as
a probably authenticated MUA is talking to you, you might accept the
message first and then bounce later to that authenticated user.
Best regards from Dresden/Germany
Viele Grüße aus Dresden
Heiko Schlittermann
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