Not sure but I think there is more than one notification system.
The company system only sends notifications of reroutes, irops, etc. Very infrequent. (if ever)

The union system is the one that sends the regular monthly reminders about bidding.

I forget how I signed up for the bidding reminders but I get them every month. Works good. The texts come from "dalcomm.alpa.org"
Maybe someone else can direct you to that dalcomm sign-up page.