Peter Hansteen writes about OpenBSD, pf, spam fighting with greytrapping, and running mail servers such as OpenSMTPD.
HN commenters link his posts on mail systems, OpenSMTPD and moving off Exim, and one finds his mail provider article especially interesting.
The redacted screenshot at https://nxdomain.no/~peter/blogpix/likely_suspicious.jpg indicates that the sending server used an IPv6 address that ends with the digits 19. The SPF record for bsdly.net includes two IPv6 addresses, neither of them ends with 19. It also includes some more things, up to three layers of indirection so I'm not sure I checked everything, but I didn't see …19 anywhere.
I suspect that what we have here is a misconfiguration at bsdly.net and perhaps a poorly chosen error message at gmail.
The big news for some of us is that Exim has been dropped from ports. Here is a good article about transitioning from Exim to OpenSMTPD:
https://nxdomain.no/~peter/time_for_opensmtpd.html
I tried using OpenSMTPD a long time ago, shortly after it came out, but things were not stable enough. I guess it is time to give it another go...
OT: This site has another recent article I found even more interesting-
A Major Mail Provider Demonstrate They Likely Do Not Understand Mail At All https://nxdomain.no/~peter/they_do_not_understand_mail_at_all.html
Gotta love the email self-hoster holdouts, mad props and respect.
Yes, some idiot keeps adding the "porn" tag to the site for some reason.
Anyway, the article in question is also available, trackerless and with "classic" formatting at https://nxdomain.no/~peter/better_off_with_pf.html - normally my WIP to show early reviewers spot.