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Apparently I installed that thing in 2006 and I last updated it in 2016, then I quit updating it for some reason that I totally forgot. Probably laziness...
It's been running for quite some time and we kind of forgot about it in the closet, until the SSH tunnel we use to get our mail outside our home stopped working because modern openssh clients refuse to use the antiquated key cipher I setup client machines with way back when any longer.
I just generated new keys with a more modern cipher that it understands (ecdsa-sha2-nistp256) and left it running. Because why not 🙂
Patience. It really helps to have all the latest set up: SPF, DKIM, DMARC. Then after that it's a matter of IP reputation, you can email the various blocklists and you wait for the rest of them to clear on their own.
I've had that IP for 10 years and it has never sent spam, and I've sent enough emails that people open that it actually does get through fine. I haven't had to think about it for a long time, it just keeps on working. Barely had to even adjust my Postfix config through the upgrades.
This is true. If you have DMARC and your RUA set up (with a working email (or one that doesn't bounce at least)) along with SPF and DKIM, Google and MS will accept your mail. The only time it won't at that point is if your IP is in the same /24 as a known spammer but so long as the spam stops, you'll fall off the list. Some of the common spamlists allow you to request your IP be removed by request and I can only recall one list that almost nobody uses that makes you pay for the removal though there may be more I don't recall.