For my instance, I already have an MXRoute account that I use for my personal email, so I just set up an account on there and pointed Lemmy at that. I’ve been down the road of self-hosting email, and it is a dreadful experience.
Granted, that was with full inboxes and POP3, just hosting the send part might not be so bad. But then you have to contend with possibly being on spam lists, and those are hard to get yourself removed from. If you have some cash to let someone else deal with that headache for you, I fully encourage taking that route.