installation problem: Authentication failure No supported authentication methods

[boxyball]

Hello,

I am trying to install roundcube 1.3.9 on Fedora 30
I keep seeing the error below when doing the ...
Test SMTP config
... part of the install:

Authentication failure: No supported authentication methods (Code: )

I been checking and rechecking sendmail/dovecot/saslauthd and cannot find a problem.
I do not see any errors in any logs.
How do I troubleshoot/fix?

[JohnDoh]

The message suggestes your smtp server does not support authentication, may be it's not required?