I have a server running Windows 2008R2 SP1 with Exchange Server 2010.  This server is a rebuild of an Exchange server that crashed in Dec. 2014 (no other information provided).  As of 3 weeks ago, users from the Central Office group are getting the "Out of Office not working, server unavailable" message".  There is also certificate popups and MailTips can't be shown for some users.  Certificate popups for the old (crashed) computer also keep showing up despite our best efforts to remove in DNS.   (Putting in as much info as possible).  There were entries in DNS for the crashed server that has since been removed.  I would appreciate some pointers on where to look in troubleshooting this issue as I am not an Exchange Administrator but quickly learning.  I have also read that there may be KBs that were pushed out that may cause these symptoms. 

Thanks in advance for your help

• Edited by GeJaeger 9 hours 45 minutes ago