I know it's not a popular topic. And there are all sorts of arguments
against MTA-STS. But, it is deployed in the wild and has an active RFC.
To those who wish to have an RFC 8461 compliant sending server, I have
created a bit of a perl solution....
https://github.com/Bobberty/MTASTS-EXIM-PERL
--
"Non sibi, sed patriae"