Mails from Debian\Dovecot are returned, why?

Question

Debian

I send a letter to my box on my server (VPS-Debian6). After a couple of seconds, it flies back.
I wrote from both mail.ru and gmail.com

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

  [email protected]
    local delivery failed: retry timeout exceeded

Wherein. From all forms on the site, letters leave and reach (to the same gmail.com).
Here is a piece from /var/log/exim4/mainlog

2017-10-13 13:05:04 1e2wq0-0005EC-1Q DKIM: d=gmail.com s=20161025 c=relaxed/relaxed a=rsa-sha256 [verification succeeded]
2017-10-13 13:05:04 1e2wq0-0005EC-1Q DKIM test passed ([email protected] domain=gmail.com), good signature.
2017-10-13 13:05:04 1e2wq0-0005EC-1Q <= [email protected] H=mail-wm0-f45.google.com [74.125.82.45] P=esmtps X=TLS1.2:RSA_AES_128_CBC_SHA1:128 S=2708 [email protected]l.com from <[email protected]> for [email protected]
2017-10-13 13:05:04 1e2wq0-0005EC-1Q == [email protected] ([email protected]) <[email protected]> R=procmail T=dovecot_deliver_pipe defer (0): Child process of dovecot_deliver_pipe transport returned 75 (could mean temporary error) from command: /usr/lib/dovecot/dovecot-lda
2017-10-13 13:05:04 1e2wq0-0005EC-1Q ** [email protected] <[email protected]>: retry timeout exceeded
2017-10-13 13:05:04 1e2wq0-0005EK-7X <= <> R=1e2wq0-0005EC-1Q U=Debian-exim P=local S=3535 from <> for [email protected]
2017-10-13 13:05:04 1e2wq0-0005EC-1Q Completed
2017-10-13 13:05:04 1e2wq0-0005EK-7X => [email protected] R=dnslookup T=remote_smtp H=gmail-smtp-in.l.google.com [173.194.222.27] X=TLS1.2:RSA_AES_128_CBC_SHA1:128 DN="C=US,ST=California,L=Mountain View,O=Google Inc,CN=mx.google.com" C="250 2.0.0 OK 1507889104 c4si278921ljd.74 - gsmtp"
2017-10-13 13:05:04 1e2wq0-0005EK-7X Completed

What else can I say.
The last thing that was done with the domain - registered dkim, dmarc, adsp
The quota package is installed.
From the logs it is clear that the matter is in Dovecot. I googled that it could also be a matter of rights. I started reading - my brain boiled.

Answer 1

DKIM, DMARC, ADSP have nothing to do with it, look for an error in the local configuration. You have problems with local delivery of letters - most likely, the transport is set incorrectly, the directory with mail dirs is set incorrectly or inaccessible, or it has incorrect permissions.
See Dovecot's log for details.