the problem seems the following.
You send a test email from [email protected] which is the same time your inbound mail (mail)box. None of the users in your servicedesk System will have this email address, which means an "error" message "You are not a valid..." is created and sent out again to this Mailbox by the outbound mail service. On the next cycle when the inbound mail checks the inbound mailbox, it finds this message and tries to attach a note or create a new incident and can't do it, because it's still not a valid user. And again an error message is sent out. You create a mail Loop...
Stop the inbound mail service, clean out the mailbox and start the mail service. Then it should be silent.
This fixed it. Thanks for your timely response.