Redmine

We are working on a Wordpress site with a plugin for contact forms. When you submit the contact form an email is send. In this case we send the email to our redmine email account.

Our redmine is setup to receive emails and to create new issues out of them. That works well.

For whatever reason redmine cannot process the email send from the Wordpress site. When I send the exact same email (from and to address and the content are the same in Contact form and the email) with my mail program then redmine receives it without a problem.

In both cases plain txt email is send.

I have no clue how to trouble shoot this further.

Any suggestion where to start looking?