After being upgraded to Buster, some hosts including mw1265, mc1033, mc2033 (but I think not all Buster hosts) have started firing systemd service alerts due to the firstname.lastname@example.org failing. Journalctl says:
rzl@mw1265:~$ sudo journalctl -u email@example.com -- Logs begin at Tue 2020-12-15 17:26:31 UTC, end at Tue 2020-12-15 23:13:11 UTC Dec 15 17:26:34 mw1265 systemd: Started ifup for eno1. Dec 15 17:26:34 mw1265 sh: Cannot find device "eno1/64" Dec 15 17:26:34 mw1265 sh: ifup: failed to bring up eno1 Dec 15 17:26:34 mw1265 systemd: firstname.lastname@example.org: Main process exited, code=exited, status=1/FAILURE Dec 15 17:26:34 mw1265 systemd: email@example.com: Failed with result 'exit-code'.
Not sure if that's an artifact of the reimage, a config incompatibility with buster, or something else. It doesn't seem to be harming anything, apart from causing the systemd icinga alert to fire, so instead of trying to just restart it and clear the alert, I've left it as-is for investigation.