The last time I implemented something like this we used a little library to check for typos on common domains and gave users a chance to correct on the front en

The last time I implemented something like this we used a little library to check for typos on common domains and gave users a chance to correct on the front end before submitting. It significantly cut down the frequency of bad email addresses. All of the other stuff is important too, but the most common issue is going to be someone tying "gnail" instead of "gmail", not having an obscure domain. On a related note, I have mylastname@gmail.com and I receive emails from other people with my last name several times every week. I am almost certain they mean to type [firstinitial]mylastname@gmail.com but miss that first character. That's my working theory anyway. I've had to intervene multiple times when getting sent important medical emails for a different person with my same last name.