Exchange on Server 2003 SBE?

After remove our IP from being blacklisted, all of our Exchange users can no longer send email to several domain (ex. gmail.com, charleswardlaw.com). In the Exchange Server queue, it says that the "connection was dropped by the remote host." I made sure our Exchange server bgslawoffices.com/68.213.178.10 is no longer being blacklisted on MXtoolbox.com. Clients are also getting the following bounce back error: There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. <bgslawoffices.com #5.5.0 smtp;550-5.7.1 [68.213.178.10 7] Our system has detected that this message is> Can someone please help? Thanks