In a word YES. As a regional manager for a major financial institution one of my duties was reading thru e mails, private, personal, work related, Bloombergs etc, etc. My company subscribed to a service that would get all communication in/out. It was sift through it for key words "bank, guarantee. promise, guess, names of any other company etc".... It would also pull out random e mails for review. I would be sent these pulled out messages, have to read through them, iniital and respond back that all was ok, if not and I found something wrong (and by that I mean anything from someone supposedly promising a client something, to an off color joke between 2 friends in a personal e mail) I had to submit a report. Some of the stuff I had to read through, was -- how do I say.... 'interesting'
Especiallly as we had a bunch of younger guys who would routinely email their friends regarding their weekend exploits.
So, be aware -- everything and anything going through your company's computer can be read AND KEPT by someone other than yourself.