Emails are not sent - Failed to authenticate on SMTP server with username

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In the last day or so I have noticed my emails are not being sent

On PS1.7.6.8

In sending test email I get error message

Error: Please check your configuration

Failed to authenticate on SMTP server with username "[email protected]" using 2 possible authenticators

And on PS1.7.7

In sending test email I get error message

Error: Please check your configuration

Failed to authenticate on SMTP server with username "[email protected]" using 2 possible authenticators. Authenticator LOGIN returned Expected response code 235 but got code "535", with message "535 Incorrect authentication data ". Authenticator PLAIN returned Expected response code 235 but got code "535", with message "535 Incorrect authentication data ".

 

Any ideas as I have not  changed any settings ??