New Post: How to mark messages as read?

I am successfully searching for messages using the "(UNSEEN)" flag, but I'm having some difficulties marking them as read or "SEEN".

This is what I've tried so far:

currentEmail.Flags.Remove("UNSEEN");
currentEmail.Flags.Add("SEEN");

as well as:

currentEmail.Flags.Remove("(UNSEEN)");
currentEmail.Flags.Add("(SEEN)");

I also tried just adding the SEEN flag (so removing the first line of code), but none of these worked - the email remains UNSEEN (unread). To be specific, this is a Google Apps (Gmail) account.

How would I go about this?