Debian 6 fresh install, ISPConfig3, dovecott, postfix.

Received this when try to send an email to the created email:

This is the mail system at host example.com.

I’m sorry to have to inform you that your message could not
be delivered to one or more recipients. It’s attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<admin@example.com>: unknown user: “admin”

Reporting-MTA: dns; example.com
X-Postfix-Queue-ID: 89D21231E2
X-Postfix-Sender: rfc822; xxxxx@xxxxx.xx
Arrival-Date: Sat,  4 May 2013 17:12:29 +0200 (CEST)

Final-Recipient: rfc822; admin@example.com
Original-Recipient: rfc822;admin@example.com
Action: failed
Status: 5.1.1
Diagnostic-Code: X-Postfix; unknown user: “admin”

And fixed like that: delete the domain example.com (my domain) from the line mydestination, leaving it like that:

mydestination = localhost, localhost.localdomain