Same Squirrelmail error here.
meticulously and revised some crucial steps.
Here's what I have gathered o far.
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)
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.