I do a lot of optin email. Here are some examples of bounced emails that people use to sign up:
These are very common errors that occur nearly every day. A regex isn't going to help here. What does help, is a notification that asks people to verify what they typed –– if the email contains an obvious, common error, such as one listed above.
mailcheck [1] is great for this, especially when supplemented with your users' most popular email domains.