Do you have the bounce message?
It could have been your mailbox was unavailable (full? Overloaded by someone repeatedly refreshing the webmail page?). When a mailbox is unavailable, even briefly, you'll start to get mailer Daemon messages.
My guess: an A/B test gone wrong.
Do you have the bounce message?
It could have been your mailbox was unavailable (full? Overloaded by someone repeatedly refreshing the webmail page?). When a mailbox is unavailable, even briefly, you'll start to get mailer Daemon messages.