Authentification failed

Hello,

All of a sudden today authentication of my emails has failed (I have not changed my email passwords). I use Contact Form 7.

The only way I can get emails to be sent via the contact form is if I remove authentication in your plugin settings.

I was previously using the “plain” authentication. Should I try using something else?

Any help appreciated. This is the error code:
5.7.8 Error: authentication failed: authentication failure