Davidm wrote:

You can get change over reed switches (google it). Wire it to use the
contact pair that closes when the magnet on the flap moves away from
the switch.

That could provide a signal of the right sense.

Does the OP need a circuit which latches, for the rare occasion
when the postie doesn't leave the mail stuck in the flap, with a
gale howling through the gap? ;-)

Chris
--
Chris J Dixon Nottingham UK


Plant amazing Acers.