I have a domain that would be great for an e-mail forwarding service, but I have second throughts about starting it... Is there someone here with experience in this area? What should the OP be most scared of?
It's fun because you gotta learn alot about email. Especially when you play with DKIM, ARC chain you found yourself reading through RFC. Or when I discover weird issue like this: https://hanami.run/blog/posts/the-quirks-of-gmail-ui/
I think the OP mail one is for fun, people who registered an emoji email properly expect some fun aspect and OK with email being lost.
In practice, the most scared thing is having your IP on blacklist. Very quickly people will complain when they lost email or too many email goes to spam or just rejected completely.
Due to the nature of email forwarding, people usually own the domain, so they use random address for many random website(coupon, download free ebooks, shitty newsletter...) so it attract a large amount of spammer I have to constantly deal with now. When gmail return a 550 in their SMTP server(550 mean they block/rate limiting), I got a bit worry at first but I learnt to live with it nowsaday
Lots of spam complaints to handle manually. Also payments using stolen credit cards.