I've been hosting three servers for over a decade and only had that problem once for a month with Google about 6 years ago. As long as you setup SPF at a minimum you'll be fine
I run my own mail server and use postmark for delivery. It is really inexpensive, I don't need to rely on Gmail for anything, and after setup has required almost no interaction for 10+ years.
Sometimes you can contact them and ask to be removed from whatever list or be allowed.
In my experience that lasts about a week, then blocks again.
I eventually gave up.
Tons of bots out there looking for SMTP serveres too, .