Markus,
Sorry for the late response, I did a quick search to find a solution to your problem.
community.dynamics.com/.../83984.aspx
This link offers some solutions to the Outlook plugin not sending emails that are in Pending Send status.
Basically it could either be a configuration in Outlook itself, or a security permission for the user running the workflow.
This may help you use the Create Record Step vs the waiting step.
Let me know how it goes =)
Jonathan Tabaka