What a piece of crap, man.
I needed copies of some escrow papers for taxes and asked my escrow company for them. They usually just send them in plain old email, but this morning they did so using MS365 encrypted messaging.
The instructions (from MS, not the escrow company) said to download the file, double click it, and use my email addy as the passcode. When I did that, I got a, "this is not a Microsoft account - would you like to create one?" Hell no I don't.
So then there was another option listed for a one time passcode. I did that and got an email with a numerical passcode. Copied and pasted. "Invalid code". Did it again. "Invalid code - too many attempts." Then I downloaded it again, asked for the one-time code, and this time just typed it in. Finally got in.
IMO, what a piece of crap system to use when working with people who might not be on MS365 or have MS accounts.