For people who are on many discussion mailing lists, the first of every month is “Mailman Day”, and has been for nearly a decade.
Mailman is the most widely used mailing list manager for discussion lists and, by default, it sends email to all subscribers on the first of the month reminding them that they’re still subscribed to the list and how to unsubscribe. This is really useful, as I’m on some mailing lists that haven’t had any traffic other than the reminders in a couple of years, but it does mean that my mailbox looks like this this morning:
Discussion lists sending reminders is a close parallel to our usual recommendations for bulk mailing lists to send something at least monthly, so that recipients remember who you are and that they’re subscribed – and so that recipients who have vanished bounce that mail, so you can eventually remove them from your mailing list. (We’re not suggesting that you send a “this is a reminder” mail monthly – create some real content and send that).
Mailman Day also means that if you’re sending mail to a technical/internet-savvy demographic and you choose to send it first thing in the morning of the first of the month, you’re competing with a lot of noise in your recipient inbox. Unless you’re mailing daily it might be worth shifting a day forward or backward to avoid that conflict.