Sorry to refloat this post. I'm having exactly the same problem nl0pat had. I tried to change the hostname and so on, but the problem still there.
Here's a copy of the error given by mail.log
May 6 20:58:48 r23523 pop3d: Connection, ip=[::ffff:18.104.22.168]
May 6 20:58:49 r23523 pop3d: chdir domain.aaa/info/: No such file or directory
And a copy of the "postconf -d | grep mydestination"
mydestination = $myhostname, localhost.$mydomain, localhost
proxy_read_maps = $local_recipient_maps $mydestination $virtual_alias_maps $virtual_alias_domains $virtual_mailbox_maps $virtual_mailbox_domains $relay_recipient_maps $relay_domains $canonical_maps $sender_canonical_maps $recipient_canonical_maps $relocated_maps $transport_maps $mynetworks $sender_bcc_maps $recipient_bcc_maps $smtp_generic_maps $lmtp_generic_maps
relay_domains = $mydestination
Maybe it is due to a step I didn't consider when following the howto. Anyway I have no installed Spamassasin, ClamAV...
Thanks in advance for your support.