IS46: Configuring inbound email

I tried to configure IS4.6 for receiving emails but it doesn’t work. Sending works fine. I set up a port for email (IMAP) and when I send an email to the IS-mailbox it is deleted after it arrives (I checked that with an email program also accessing the mailbox). That’s ok, I configured the service like that. Then my flow in IS is called (only contains savePipelineToFile) and it creates a file which is empty (Size 1kb - contains only parameter filename).

What is wrong? Where is my email (which IS deleted on the mail-server)?