returned mail: 550 error


Oct 14, 2006
Since yesterday, when i send email to any of the mail accounts created for our website (replaced by xxxxxx) it gets returned with the message i include. It's the first time it happens, and i have no idea how to fix. It's cPanel Build 10.9.0-STABLE 45.
I'd appreciate any help!

----- The following addresses had permanent fatal errors -----
<[email protected]>
(reason: [] is currently not permitted)

----- Transcript of session follows -----
... while talking to
>>> DATA
<<< [] is currently not permitted
<<< 550-to relay through this server. Perhaps you have not logged into the pop/imap
<<< 550-server in the last 30 minutes or do not have SMTP Authentication turned on
<<< 550 in your email client.
550 5.1.1 <[email protected]>... User unknown
<<< 503 valid RCPT command must precede DATA