Sending secure emails

Hi,

I have a custom application in Azure. The application needs to send emails to users in my Office 365 tenant. I configure the application to use smtp.office365.com at port 587 which I believe should use SMTP over TLS hence it's secure.

1. Does this guarantee the email submission is not plain text?

2. Does it secure the connection before sending the user credential for authentication by O365 SMTP server?

Thanks.