550 relaying to (recipient email) prohibited by administrator

[Guest]

I can recieve mail, but when I send I get the message "550 relaying to
(recipient email) prohibited by administrator" returned.

 

[Gordon]

I can recieve mail, but when I send I get the message "550 relaying to
(recipient email) prohibited by administrator" returned.

Are you authenticating your SMTP server?

 

[Vanguard]

I can recieve mail, but when I send I get the message "550 relaying to
(recipient email) prohibited by administrator" returned.

Off-domain port 25 (SMTP) traffic blocked to thwart spam from spamming or
infected customers:

http://www.commercestreet.com/Blocking_Port_25.htm
http://help.yahoo.com/help/us/mail/pop/pop-38.html

http://www.postcastserver.com/help/Port_25_Blocking.aspx
http://www.aota.net/Troubleshooting/port25.php4
http://www.spamhaus.org/faq/answers.lasso?section=ISP Spam Issues#133
http://www.findarticles.com/p/articles/mi_zdewk/is_200406/ai_ziff129473

http://www.google.com/search?q=+block++"port+25"++SMTP++spam