Well you can't monitor what people send you but you can ensure that this won't cause you problems by setting the maximum size you will recieve on an account.

This is easy in most mail clients (such as outlook) through the mailbox options. So if this is set to 100KB (a reasonable amount) and a message exceeds that value then the header info is downloaded. You read the header and decide to either delete it, retrieve the rest of the message, or you can wait until a more condusive time to download (like when you are connected to a high-speed).