Sites like mail-tester.com, learndmarc.com, or sending a mail to ping@tools.mxtoolbox.com (which will reply a report to you) are pretty useful for that.
But yeah I have only limited experience I suppose. Having some mail correspondence with friends in the hopes of improving my domain's reputation to those mail servers.
Oh and btw, I relay through my cloud providers mail delivery system - doing it from your own IP is probably a whole different league.