Thanks for your quick answer.
Here are the informations that you asked for:
- the user has admin-permissions for the shared folder
- the problem occured undependend to an attachment also for mails without files attachment
In bugzilla where I have reported the problem, someone asked if the folders where shared before the upgrade to 7.x. The answer is yes. I will try to delete the share and share it again. Maybe this solved the problem.
Best regards
Steffen