Julie,
If your org has Fusion there are ways to create html emails that can be triggered and sent to Workfront users. Workfront isn't designed to be an email system but it does send a lot of notifications so it has some capabilities. There are limitations even if you had Fusion and can trigger these emails, such as it can only send to users registered in your Workfront (no emails to Mom) and there is no capability to attach files (but you could have a link to a file in Workfront) to these triggered emails...again, the system is designed for simple notifications to users that are managing their work in Workfront.
Might not be what you wanted but hope it shed some light; we can't connect to our M365 either so this is a workaround we've done for many of our use cases.
