Will this work? Adding an alias domain and moving primary domain MX to M365

[Telliott06]

So we have a special extenuating situation. We have a business we've had for 20 years using example1.com and we're being forced by our contract to switch and use M365 encrypted email but the entire business runs on Google Workspace. My idea is to buy a second domain example.com and add it as an alias in workspace with the MX records connected to Google and switching the primary domain MX to M365. So all future email is handled on M365 but users can still login to Workspace using @example1.com and still use all Google for our business as we have for 10 years. 

• The question is, will this work? I have apprehensions that some purchased add-ons, like Form Publisher may break on things like their workflows with email notifications. And lap GCPW is used on computers. 

• Will we still receive notifications on M365 for Google doc approval requests using Google workspace? 

• Will comment notifications still be sent to users on the M365 email?

• Does GmailApp.sendEmail still allow you to change sender to your alias domain instead of primary?

[icrew]

You can leave your Google Workspace instance set up as example1.com, but turn off Mail (and Calendar--doing calendaring across Google and MS is a recipe for intense pain) in Google after migrating the contents of Mail and Calendar to MS.

Unlike MS, Google does respect MX records, so yes, the notifications from the other parts of Workspace will go where you tell them to go. (Google has even historically sold versions of Workspace that don't include Mail--I'm not sure if they still do.)

Hope that helps,

Ian