there is a setting where you can delegate read privileges in exchange server. he doesn't need to be logged on as admin. besides which even if he was logged on as admin he'd have first have to have delegated control to the admin user -so would more than likely just given his own account access.
you can grant any privileged level from read, move, delete, he could even grant himself permissions to send on behalf as you, so e could even send emails from your address.
and there is a chance that when you signed your contract you also signed an IT use policy that generally says that your company can access your emails for the purpose of monitoring/backup. also when you leave, most companies require that you don't delete your emails, so that they can access them for business purposes (since all the work you do belongs to them).
I shouldn't worry though, most companies don't mind light and occasional use of corporate email to send personal emails.
but they would mind of you were sending out hundreds of emails with massive attachments, or sending stuff that would be considered spam, leaking company secrets etc...
