Outlook {Send Error}

-Im getting the error below with all my pop email accounts while sending emails.
-This error is happenind on some computers, & not on all computers. it worked with one of my friend's computer.

-Is it a connection problem? or a software problem?

-I tried to disable firewalls, norton anti-virus, norton internet security, still the same, nothing changed...


The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was 'pacoabinahed@hotmail.com'. Subject 'Hello', Account: 'ALIEN DJ', Server: 'mail.aliendj.com', Protocol: SMTP, Server Response: '550 Can't accept for hotmail.com ... not a gateway', Port: 2525, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC79