Office365 account - SMTP

I have this error, although I followed the FAQ and the credentials are correct.
I get messages, but I can’t send.

Whomever is the admin for your email server has a setting disabled that prevents you from sending email.

Usually done to prevent password guess attacks done against the mail receiving service.

Strange, because I can send messages from PCs, fixed and portable, where I use Thunderbird and Gufo. Both with Linux and Windows.