SENDING EMAILS ERROR CODE

Hello,

I do receive my emails on my Libertysurf mailbox under Free, but I can’t send any; here is the error message I get:

Technical details
SmtpSubmissionPermanent5XXException: SMTP send failure. Server "smtp.free.fr". Port "465". --> Unexpected SMTP server response. Expected: 235, actual: 535, full response: 535 5.7.8 Error: authentication failed: authentication failure Error code: 40ef

Could you explain how to fix the problem?

Thank you
Have a good day;