Hi again Linux00
From your description I'd say that the problem is either user or machine specific.
Next two steps I'd take..Firstly move the machine to another network point to eliminate any issues on the infrastructure. If it still doesn't work, try to login another user and see if his mail works. If it doesn't then the machine is the culprit. Start with the patch cable and work your way backwards, replace the NIC with a know good one and so on. I've known NICs to behalf inconsistantly causing lots of starnge issues.
If all else fails do a total system rebuild, it will probably be quicker than trying to solve the problem.
If it does work with another user, then the Exchange system needs to be checked out. You could try disconnecting the user from his mail box and reconnecting - I've know this to work. Alternatively, exmerge out the users mail to a .pst file, delete the mailbox and purge the system.
Recreate the user mail box and try to login again. If it works, exmerge his pst file back into the new box.
Let me know how it goes.
Regards
MD