I was trying to make a mailing list for not content on my own server yesterday and ran into the need for a reverse DNS record. Without it, mail sent from my server will be accepted by some mail servers, but will be rejected by Gmail.
My domain registrar, Hover, doesn't handle reverse DNS (PTR) records. So, I have to choose between:
1) Changing registrars or getting an additional one
2) Using something like Tinyletter, which I use for my existing mailing lists, and having a process on my server email to Tinyletter. I have to hope that Tinyletter will accept email from a server without reverse DNS and that there won't be any weird formatting issues. Or that forwarding from Fastmail (which does accept my server's email) works.
The downsides of #2 are exposing users' emails to a commercial entity (which I already do to newsletter subscribers) and the possible impermanence of the service.