Default signature per email address not email account In Apple Mail, there is functionality to add additional email addresses per email account. In G-Suite (and I would assume Office 365) you can set up email aliases and the additional email addresses in Apple mail associate with those aliases.

My issue is the need for a different email signature to be set by default for each email address, not account.

As you can see here I have multiple email addresses for this one account.



And here you can see that this account has two email signatures, but I can only set one of them for both addresses.



What options do I have to fix this?
Based on several hours of research and digging around in .plist and other files, I feel confident that there is NOT a way to do what you (and I) are looking for in the Apple Mail macOS app. Sorry.

Here's another answer that helps confirm this.

This would be a handy feature that couldn't possibly be very hard for Apple to implement based on how they have already designed a very flexible UI for assigning signatures to accounts, and the structure of the underlying .plist files seems conducive to the concept, too, if the aliases just had account-like IDs. Too bad.