OAB is not updating for one user only. what logging can I enable to see what is causing this?also are therelimits in terms of number of folders and items a mailbox can have? We use Zantaz EAS for archiving and once we created shortcuts for all archived emails in outlook - it simply couldn't handle it (16249 folders and 481435 items). Subsequently we removed all shortcuts(stubs) from the mailbox, but it would be helpful to know what limits are there if any...

Probably the mailbox in question was either not restored correctly or was likely corrupt. Take PST backup of the mailbox.Try removing the exchange attributes (exchange Tasks in ADUC) for the user object and recreate a new empty mailbox and associate with the user object. Need to check on limits.