Comment 3 for bug 1658370

As of March 12, 2017 we got a PTR record for 69.195.146.38 mapping to mixxx.org. The rate of mail rejects dropped precipitously on that day based on our postfix logs.

The only rejected emails I've seen after March 12th (other than normal stuff like accounts no longer existing, full mailboxes, etc.) have been from AOL, e.g.:

Mar 20 07:31:03 mixxx postfix/smtp[25097]: 5B8098029B: host mailin-02.mx.aol.com[152.163.0.68] refused to talk to me: 554- (RTR:BB) https://postmaster.aol.com/error-codes#554rtrbb 554 Connecting IP: 69.195.146.38

telnet'ing to an AOL mx prints the following:
$ telnet mailin-01.mx.aol.com 25
Trying 64.12.91.195...
Connected to mailin-01.mx.aol.com.
Escape character is '^]'.
220-mtaig-mac03.mx.aol.com ESMTP Internet Inbound
220-AOL and its affiliated companies do not
220-authorize the use of its proprietary computers and computer
220-networks to accept, transmit, or distribute unsolicited bulk
220-e-mail sent from the internet.
220-Effective immediately:
220-AOL may no longer accept connections from IP addresses
220 which no do not have reverse-DNS (PTR records) assigned.
421 4.4.2 mtaig-mac03.mx.aol.com Error: timeout exceeded

But we do have a PTR record.
I submitted a postmaster ticket with AOL using this form:
https://postmaster.aol.com/sa-ticket
We'll see what they say.