My ISP unexpectedly stopped permitting SMTP relay of non-ISP domain names, after 22 years.

I have a wildcard subdomain MX entry in my DNS, such that sending/receiving *.example.com are valid.

I do this so I can email from a email address, say [me@reddit.example.com](mailto:me@reddit.example.com) , tailored to the recipient. Great for knowing who leaks my email address, and can even create a MX record for that subdomain and point it to 127.0.0.1 so the spam never even gets to me if I wish.

So now I'm looking for a low volume STMP relay service, that will of course verify I own my domain name, but doesn't require me to manually add each subdomain (of which there are countless).

Any recommendations?

Thanks!

edit: only looking for outbound relay - I'd still be receiving/hosting inbound directly.