Apologies if this is in the wrong forum - if it is, could some kind sysop move it to the correct place so that it gets seen by the right people.
The current msmtp package is v1.8.19. This is now over 2 years out of date and missing a vital new setting "set_msgid_header".
v1.8.19 does not create this header ("messageID") which is now "watched" by a lot of spam filters and large mail providers such as GMX.
TIA