cmwetherell Any mail provider will work usually, we have our own mail server here at Flarum we send from. However google, yahoo, sendgrid, etc. are all valid email services as well using SMTP.
I do want to make clear though that running your own mail server is not an easy task and requires a ton of patience and constant maintenance with blocklist, invalid anti-spam list, etc. it's for sure not for everyone and generally speaking I would personally highly recommend using a 3rd party service unless you have a large amount of time to dedicate towards maintenance and very deep learning about email systems.