I'm probably the only holdout at this point too.
I was using Mail because it was easy and I could have my main email accounts open to swap between without having to log in/out of Gmail in my browser. Yet now I see that Mail has no idea how to send emails and kept sending a majority of my resume emails from my personal account while having those emails sit in both the professional and personal sent boxes. Basically, I have no idea which account actually shows up on the other end now. If it was the personal account then it's no wonder I haven't heard back from anywhere.
So now I have a client solely to use for professional stuff. And I double checked my most recent submission to make sure it sent from the correct account.