meaning

In fact, the modals "must" and "should" can be used in the definition of this verb form ; it is considered to be an auxiliary.

(OALD) 5 be to do something used to say what must or should be done ♦ I am to call them once I reach the airport. ♦ You are to report this to the police. ♦ What is to be done about this problem?

TOPICS: Permission and obligation

There is however a second meaning of this auxiliary.

(OALD 6 be to do something used to say what is arranged to happen ♦ They are to be married in June.

It follows that in the case of this indication about an email address, there may be a difference or there may be relatively little. It depend on the procedure which precedes. If, in order to suppress the address, certain requirements must first be complied with, then this prerequisite can be seen as an arrangement between user and sevice provider; in this case the meaning is not that the user sees the supppression as a necessity (although the necessity is a reality) but it is instead "the suppression will be carried out as compliance with the preliminary steps makes necessary".