Happy New Year ... and help with email problem please

[cherry777]

Hi all

Having a problem with email with the following error please help

Results

The mailing function returned an error while trying to send the mail.

The following errors were outputted by PHP when attempting to send mail: PHP User Warning: 535 Authorization to the SMTP server failed in ..../includes/class_mail.php on line 715

Thanks. Running PHP version 5.6.30

[Mark.B]

The credentials used for the mail server are incorrect, or the mail server is otherwise refusing the connection.

[cherry777]

Thank you