A transmitting mechanism for indicating the deposit of mail into mailboxes having doors that pivot about a horizontal hinge. Such mailboxes normally identified as curb side, wall mounted, and slot type. The transmitting mechanism is comprised of an adjustable knob capable of positioning an adjoining tilt switch, such that the mechanism can be set to send a signal at any preferred mailbox opening. As the mailbox door is opened past a predetermined angle, the tilt switch completes a circuit which emits a signal to a remote receiver which activates a sound and visual alarm indicating that mail has been deposited in the mailbox.