Using SMTP directly by-passes office 365 or any other client. It is what the servers (not outlook, thunderbird, but exchange, or postfix) uses to send an email. I have forgotten what your first post asked for but SSL (TLSv1.x) is what is used to talk to a server. In this case you are becoming the server by using SMTP. The only real issue is if you are not on the same IP of the mail server which then looks like you are relaying mail.

Johnf