I have sent an e-mail from a web server using PHP SMTP server and i received Mail delivery failure e-mail back:

From: Mail Delivery System <[email protected]>
Subject: Mail delivery failed: returning message to sender

[email protected]
host mail.somedomain.com []
SMTP error from remote mail server after RCPT TO:<[email protected]>:
554 5.7.1 <[email protected]>: Relay access denied

Action: failed
Final-Recipient: rfc822;[email protected]
Status: 5.0.0
Remote-MTA: dns; mail.somedomain.com
Diagnostic-Code: smtp; 554 5.7.1 <[email protected]>: Relay access denied
Any idea what is wrong?