Yes, sure, self-hosting email can go fine for a long time, depending on the amount of users that you have and what your users do (For example : try bulk email) and whom they want to email with, or send emails to mailing lists, or use email forwarding. The OP wants to run a Lemmy instance and have email out working, probably just for notifications. Using a transactional email provider for the latter seems like a sensible choice to me.