(That's approximate descending order of value, to be clear. In particular, if you don't have a matching PTR record, you're hosed whatever else you try to do.)
Re:Dovecot audit complete
by greglindahl on Monday January 16, 2017 @01:42PM
(#13411929)
Looking at the incoming mail in my server, I discovered that there are big legit mail senders who have a non-matching PTR. I suppose that at some point gmail et al stopped using that rule, or they just look for certain patterns in the PTR name, or something.
Beyond that, the main deliverability improvements, in approximate order of value, are: PTR record with the hostname you send mail from; DKIM; SPF; DMARC.
My mail server runs all of these, and I've yet to encounter trouble sending to anyone, including Gmail, which is often mentioned in threads like these as being a special issue. Admittedly I've been running mail from that IP since 2004, so have a long history of not being a spammer, but as long as you start out with a clean IP and keep it so, and make sure all your sender legitimacy boxes are properly checked, I don't see any reason why you should have undue difficulty.