I upgraded my mail server to exchange 2010, the challenge I have is that exchange still has records of the old mail server and some users are failing to authenticate.

Hi, You cant get an answer with like this post, we need more details on your issue to help you. You can use the exchange 2010 forum instead of this one (2013). http://social.technet.microsoft.com/Forums/en-us/exchange2010

Yes, this is the Exchange 2013 forum but maybe a mod can move the discussion to the proper section. I hate to answer a question with another question (more questions) but I think we'll need some more information. First, it might be useful to know from what version you migrated to Exchange 2010. 2003? 2007? Second, can I assume you've installed E2K10 on a separate server and are now waiting to move elements over? 1. Exchange still has records of the old server. Where? In DNS? In the CAS URL settings? 2. Users failing to authenticate may be due to CAS URLs not matching what is on the certificate... and speaking of certificate, have you exported the one you had (?) on the Exchange (version?) server and imported and enabled it on the E2K10 server? It would help if you provided some more details about the procedure you followed and where, exactly, you are now in the migration. Otherwise, we'll just be guessing and making assumptions.Please mark as helpful if you find my contribution useful or as an answer if it does answer your question. That will encourage me - and others - to take time out to help you.