Digging through the logs:
for f in /var/log/mail*; do echo "###### ${f}"; zgrep -i "\(error\|unable\|cannot\)" "${f}" | tail -n 5;done
I found:
###### /var/log/mail.log.1 Mar 1 03:44:57 biowikifarm sm-msp-queue[19260]: 01P2QEMB026968: 0212e1ag019260: sender notify: Cannot send message for 5 days ###### /var/log/mail.log
… and a lot of:
Mar 3 00:42:23 biowikifarm sm-mta[7129]: STARTTLS: write error=syscall error (-1), errno=32, get_error=error:00000000:lib(0):func(0):reason(0), retry=99, ssl_err=5
… errors. Older logs reported:
###### /var/log/mail.err.1 Oct 11 16:22:11 biowikifarm sm-mta[13013]: w96JF7Cq013599: SYSERR(root): Cannot exec /usr/sbin/sensible-mda: No such file or directory
I have no idea if this is fixed yet or not, but yesterday (March 2. 2020) the service did not work at all and only a
sudo service sendmail restart
resolved the issue temporarily. Should we create a cron job or is there a cron job already?