"Requested action not taken: mailbox unavailable"

[Gu3rr1lla]

I cant receive any emails and i get this error message when trying to send email:

ERROR:
Message not sent. Server replied:
Requested action not taken: mailbox unavailable
550 Verification failed for <username@domain.com>
No Such User Here
Sender verify failed

Im using squirrel mail. Any ideas?

[Infopro]

Have you actually created an email account, or are you attempting to use the default "account".