What is the best way to verify that an e-mail address belongs to a business ("work") domain? For example, I don't want _john.doe@gmail.com_ or _jane.doe@outlook.com_. But I do want _johnny@apple.com_ or _ma.baker@thebakercompany.com_.

The first thing that comes to me is to have a rule to exclude gmail.com, outlook.com, yahoo.com, but there are huge amounts of those and it feels stupid to me.

Any thoughts?