In what must be one of the weirdest flexes ever, I can proudly say that I keep my own email server. And like everyone who keeps their own e-mail server can attest, GMail is always annoyingly difficult to work with.

The last version of this problem is that GMail stopped receiving my email because I didn't have a PTR record, an error that's annoyingly difficult to debug for two reasons: because the record is not really called "PTR", making it slightly difficult to figure out what they want for me, and because I know I've had one for years.

Long story short, the problem was that my server started using IPv6 and the outgoing address was not matching the IPv4 PTR record I had. So I solved the way these problems are always solved: I turned off IPv6 and everything works again. I can't remember who gave me this advice for the first time, but I can confirm that it works.

Now, if only I could manage to identify why Apache is not redirecting the LetsEncrypt challenges properly...

Edit: This post is best read when listening to Future Boy's "Computer Shop". Warning: NSFW language!