[exim] Software caused connection abort

exim-4.68-0 on freebsd current

in the last ten days of logs, i find over 5,200 instances of "Software
caused connection abort." googling the list says it comes from delaying
spambots, yet i have no delays at all.

any other clues? i am chasing occasional deliver failures from inside
google to one of my servers, and one synced with such an entry, if ntp
is to be trusted.

any