Scheduled reminders worked last year, but are not working this year.
I had made some changes to the Outbound Mail settings, but a) I set these back as they were and b) test emails come through just fine.
To sidestep the issue of 'day before membership end date', I entered today's date. When I manually executed 'Send Scheduled Reminders', the system reported that the job had completed, but no emails were sent and no errors were logged.
I just learned that things are not quite as 'simple' as I had hoped: At least one person received the reminder that I manually sent, but at least one person did not. I am among the 'at least one who did not' and I know that there are absolutely no email filters on the recipient side - so what happened?