It's good taht you asked this before trying it. For starters, you would need to escape that . in your regex.

Second, I'm going to agree with broquaint and davis on this. Your regex will most likely bomb on my email and the email addressses of my co-workers. All of us are first.last@ but the domain changes. Some are company.com some are sudomain.company.com. You can see how this can get crazy very quickly.

Be lazy, download a module. It spares you pain.