The big email issue is forwarding an email that you receive to email@example.com. Go ahead and try it for something simple. I believe discourse reads the email and does something clever, like everything after "forwarded message" is discarded.
If you forward an email with comments inline or at the end, all of that disappears.
If you're an admin, on the forwarded emails, you can see the original content by finding the envelope icon on the original post and clicking. It shows what was emailed and you can back it out of there, but it's a pain.
@ariddell, want to give it a try?