hi. could some one please help me i am running postfix mail server with dovecot imap server i have set it up an using the email lee@xtcservers.mine.nu an it sends an receives fine except when i use outlook i am using roundcube webmail but that is another problem. My main problem is i made a new user for me friend using the username R.Walker and i cant seem to send mail to that address but i can receive mail on that address when trying to send it comes up with this error,

"Your message did not reach some or all of the intended recipients.

Subject:
Sent: 9/23/2008 11:56 PM

The following recipient(s) cannot be reached:

'R.Walker@xtcservers.mine.nu' on 9/23/2008 11:56 PM
550 5.1.1 <R.Walker@xtcservers.mine.nu>: Recipient address rejected: User unknown in local recipient table.

I don't no what the problem is if some one could help me that would be great.