We just changed over from a Windows server to a Unix server. Since the switch we aren't able to send any mail out, it is all being held in queues in exchange. Most of the time theuser isn't recieving an e-mail showing that the e-mail hasfailed. The e-mail is not hung up in the outbox and it shows as sent. When I am looking at the queues I can't force a connection to get them through. Any help would be greatly appreciated.Thanks

Is Unix server running as a smarthost? If so how authentication works for it. You may need to reconfigure the mail flow with new IP address (if changed) and new authentication (if unix server requires). How to Configure Internet Mail Flow Through Exchange Hosted Services or an External SMTP Gateway http://technet.microsoft.com/en-us/library/bb738161.aspxAmit Tank | MVP Exchange Server | MCITP: EMA | MCSA: M | http://ExchangeShare.WordPress.com

Yes, please check the authentication settings on both servers as Amit suggested. At the same time, please use queue viewer to see more information about the problematic queue and let us know the result. Additionally, what's your Exchange version? A related article: How to use Queue Viewer to troubleshoot mail flow issues in Exchange Server 2003 http://support.microsoft.com/kb/823489/en-us Thanks, Elvis