How to delete all mail on an iPhone from a computer?

I have deleted a gmail account on my computer, but I need to know if this will delete the mail on the iPhone. My boss has confiscated it and I can't let him see what is on. Will the mail still be visible on the phone, or will it automatically delete the account when it connects to the internet?

It should automatically delete the account and content from the phone when it is next connected to the internet. But be warned if he turns it on without a connection he can browse all he wants through the mail and setup a recovery if they see fit.