PTR lookups has been a thing for email servers for a very long time... "used to work fine" would have been early 2000's as far as I can remember.

PTR is de facto requirement for over 20 years now. So unless you're talking about pre-turn of the century, not really... email servers haven't worked without PTRs for a very long time.

I had to look it up, but Yahoo and AOL implemented PTR checks in 2003-2004. Gmail had it out of the box in 2004.

Can you run a server without it? Yes... and it will work with any other server that doesn't mandate valid PTR records. But no major consumer email server has supported receiving mail from a PTR-less server for 20+ years now. So you're not going to be able to email basically anyone from your server.