i noticed i have these also, can't remember i had them with version 11.5.4, but with 12.1.1 i certainly do:
Sep 11 16:00:01 bigip-01 err sSMTP[2451]: Unable to locate mail
Sep 11 16:00:01 bigip-01 err sSMTP[2451]: Cannot open mail:25
Sep 11 16:05:01 bigip-01 err sSMTP[3056]: Unable to locate mail
Sep 11 16:05:01 bigip-01 err sSMTP[3056]: Cannot open mail:25
Sep 11 16:10:02 bigip-01 err sSMTP[3328]: Unable to locate mail
Sep 11 16:10:02 bigip-01 err sSMTP[3328]: Cannot open mail:25
can't really remember i ever configured email for something, anyone have a clue where to start looking?