EddyMo on "[Plugin: Knews Multilingual Newsletters] Cannot send mail anymore"

Since I've updated my KNews I cannot sent any mails anymore.
I guess it's because in the settings of the smtp-server are the fields "SMTP User" and "SMTP Password" filled in.
I cannot clear them; when I try to and press "Save" the previous values come back again.
Also; testing the SMTP-config doesn't work because knews tries to use authentication which the server doesn't support.

https://wordpress.org/plugins/knews/