#5.5.0 smtp;550

           There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            <mail.thhill.com #5.5.0 smtp;550- blocked by ldap:ou=rblmx,dc=worldnet,dc=att,dc=net>

is this my side or his
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SembeeConnect With a Mentor Commented:
The recipient is blocking the sending server because its IP address is on AT&Ts blacklist.
That address doesn't appear in any of the major public blacklists, but it does look like a home user address. It is a problem that the operator of that sending server needs to resolve

THHILLAuthor Commented:
it is just to this one user @att.net
It appears as though he or his ISP is blocking messages from your IP address ( from being delivered.  It is possible that the IP is on a blacklist.
Sorry, left the reply window open so my first reply is not helpful.  Anyway, I would suggest you contact "abuse@att.net" to inquire why they are blocking your server.
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