You can use php to send out mass emails (html and plain text). Most spammers use this method because it's cheap and easy. You're not trying to start spamming people are you?
I really don't recommend using an image map. Some people don't have html enabled for their inbox. They wouldn't be able to see anything, in that case.
Best thing to do is to use as much text as possible, and less images. The message will load faster that way too.