If you have installed the Microsoft Authenticator app on Android or iOS, and compose and email, as soon as you send the email using the eM Client mobile app, you will then instantly get the MS Authenticator popup window at the bottom appear as per the Droid screenshot example below asking if you want to save the address.
The problem is even if you choose save, it still pops up and asks you again the next time even if it’s the same email address which is annoying.
The way to turn off this save address pop-up appearing all the time when sending mail, is to go into the Microsoft Authenticator app on your mob device and go to “Settings / Choose Info to Autofill” and (set the addresses option to "Autofill only), rather than the default of “Save and Autofill”.
eM Client appears to be the only Droid / iOS mail app I’ve used so far where this happens when sending mail. I think this is a MS app issue.
MS Authenticator should really have an eg: exclude app option within the Autofill app area rather than having to change the option to Autofill only.