X-Postfix loops back can't receive email: Dovecot + Maildir

I seem to be having an issue receiving emails. For example, I sent an email from a gmail account to my user@domain.com account and I received this email titled "Undelivered Mail Returned to Sender" at my gmail:

> This is the mail system at host li111-11.members.linode.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

(expanded from <user@domain.com>): mail for li111-11

loops back to myself

Reporting-MTA: dns; li111-11.members.linode.com

X-Postfix-Queue-ID: 4D64E1A74A

X-Postfix-Sender: rfc822; myemail@gmail.com

Arrival-Date: Thu, 16 Jul 2009 19:04:11 -0400 (EDT)

Final-Recipient: rfc822; user@li111-11

Original-Recipient: rfc822;user@domain.com

Action: failed

Status: 5.4.6

Diagnostic-Code: X-Postfix; mail for li111-11 loops back to myself

My mydestination in postfix looks like this:

mydestination = li111-11.members.linode.com, localhost.members.linode.com, localhost

The last setting I made was in my Virtualmin going to System Settings > Module Config > Defaults for new domains labeled "Include domain name in usernames?", which I selected "Only to avoid a clash". Not sure in what file in my system that change was made by Virtualmin. I did that so that the email addresses of users would be user@domain.com instead of user.domain@domain.com. The setting worked. However, this issue has come up. Any ideas? Let me know if you'd like to see any error logs, etc.

__Mozilla Thunderbird v2.0.0.22

Dovecot v1.1.11

Postfix v2.5.5

Procmail + SpamAssassin

Webmin + Virtualmin

Ubuntu 9.04__