I am trying to send emails to a user. The mails bounces back with the following NDR:-
Your message did not reach some or all of the intended recipients.
The following recipient(s) cannot be reached:
user (firstname.lastname@example.org) on 11/10/2008 11:24 AM
There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<mydomain.com #5.5.0 smtp;550 No such user - psmtp>