Question : my ip is blacklisted and when i remove it it comes back

we have in our server  Microsoft exchange version 6.5, and when we try to send people messages they comes back, i check my IP and i find it that its listed in the XBL. I go to cbl.abuseat and i remove it. but after few hours or one day i have the same problem and its listed on the same site.
I have full license of Worry-Free Business Security Trend micro version 6 and i did scan the server from the viruses or spams and still i have the same problem.

Please help me how to avoid this problem and i dont want to be listed anymore
Thank you

Answer : my ip is blacklisted and when i remove it it comes back

Hello flf4ea,

Test your mail server  here : http://www.abuse.net/relay.html
Use this link : http://www.mxtoolbox.com to see where you're blacklisted.
Read my first post here : http://www.experts-exchange.com/Software/Internet_Email/Email/Anti_Spam/Q_24944356.html

Regards.