Same Squirrelmail error here.
meticulously and revised some crucial steps.
Here's what I have gathered o far.
May 13 01:31:28 mail imapd: Connection, ip=[::ffff:127.0.0.1]
May 13 01:31:28 mail authdaemond: authmysql: MYSQL_SERVER nor MYSQL_SOCKET set in/etc/courier/authmysqlrc.
May 13 01:31:28 mail imapd: LOGIN FAILED, email@example.com, ip=[::ffff:127.0.0.1]
May 13 01:31:28 mail imapd: authentication error: Input/output error
May 13 01:32:09 mail postfix/qmgr: 0DD4A18A167: from=<firstname.lastname@example.org>, size=764, nrcpt=1 (queue active)
May 13 01:32:09 mail postfix/qmgr: D3C3A18A163: from=<email@example.com>, size=786, nrcpt=1 (queue active)
May 13 01:32:09 mail postfix/proxymap: warning: connect to mysql server 127.0.0.1: Access denied for user 'postfix'@'localhost' (using password: YES)
Nowhere in the howto is an instructio to add user postfix to mysql, it must be noted.
Moreover, when i run mailx firstname.lastname@example.org
, apparently the message is sent (or at least queued)
May 13 01:48:20 mail postfix/smtp: DE2AC18A169: to=<email@example.com>, relay=127.0.0.1[127.0.0.1]:10024, delay=26, delays=0.02/0.01/0.01/26, dsn=2.0.0, status=sent (250 2.0.0 Ok, id=01422-01, from MTA([127.0.0.1]:10025): 250 2.0.0 Ok: queued as 2E2E018A16A)
May 13 01:48:20 mail postfix/qmgr: DE2AC18A169: removed
May 13 01:53:20 mail postfix/smtpd: timeout after END-OF-MESSAGE from localhost[127.0.0.1]
May 13 01:53:20 mail postfix/smtpd: disconnect from localhost[127.0.0.1]
although it never gets delivered, therefore /home/vmail/whatever.tld/whatever is never created.
Lastly, although I am behimd a NAT'ed XEN guest, iptables on dom0 is reroutimg everything correctly.
Moreover, I believe the issue lies within the domU itself. Doesn't look like a networking misconfiguration.