Failed smtp server

email was working well on my server until I was asked to change by AWS.

I am getting this errow and can no longer sent email. AWS said nothing is wrong at their end.

Here is the error:

Failed to authenticate smtp server with username "....." using 2 possible authenticators. authenticator login returned expected code. The authenticator PLAIN return expected response code 235 but got code "535", with message 55 authentication credentials invalid.