Mophilly
What changes did you make to the server yesterday or the day before or the last few days ie since you last successfully accessed the admin mail ?
Take a look at various log files to see if there are specific error messages &/or clues, look around the time you try to access admin mail
eg messages log file, yum log file
If there is a correlation with a recent update then you should lodge a bug teport immediately so proper investigation can occur.
Also you should not start making changes to the server (rebooting etc) as the forensic trail can be lost
Bug triage experts probably want to see the status of services etc before you reboot & reconfigure etc, so maybe it is best you go straight to bugzilla anyway, & please advise the bug number here so the problem can be followed by others.