For some reason the normal contact form won't work. It doesn't send any mail to any address I request. Therefore, I used the module Webform for Drupal 7.
The problem I have is almost the same described in this thread.
However, for me the problem is even when the domain name is the same. Like
email@example.com works, but
When I do send to a gmail account, there also is no problem.
firstname.lastname@example.org doesn't seem to be 'supported'.
All the other email addresses do work.
The domain-email is hosted by Gmail. (A Google Business account)
What am I missing?