My mail server has been sending mail with no rejections from gmail until recently. No changes have been made that I am aware of.
Recently my outgoing messages are failing with an error about a "missing PTR record". I do have a PTR record setup. However, the forward lookup for the IP address and the PTR record are not the same. I saw that Gmail wants the forward and reverse lookup to be the same. That was not the case for my mail server. I changed the PTR record to be the same as the forward lookup's IP address but I still have the same problem with Gmail rejecting that server's mail.
I don't believe waiting for TTL is part of the problem. I've come to realize popular providers such as Gmail do not necessarily respect TTL. My PTR has been setup for a long time the way it is, and it always worked. So unless Gmail has implemented a new policy in this regard, TTL should not be the issue.
I've setup some domain names to use this particular IP in
/etc/mailips. While those domain names are hosted on a different IP on the subnet, they are sending mail from the one mail server IP Address. I have CentOS and Exim as the MTA.
Why would Gmail reject my email suddenly when nothing has changed? Why would Gmail be rejecting my emails as not having proper forward and reverse DNS records when they do?