Email is quintessentially "fire and forget" message passing, so there's no way to guarantee mail has been delivered and no way to "pull it back". You can embed

Email is quintessentially "fire and forget" message passing, so there's no way to guarantee mail has been delivered and no way to "pull it back". You can embed tracking in your email to see if it's been opened, and not resend in that case, but this will be flakey as it's easy to disable email trackers.