No email is send using Assignment Rules when Lead is created from external system. The LEads is assigned to the correct Queue. When I do manual LEad creation the Mail is send. Why is that

We add the Apex code: dmlOpts.EmailHeader.triggerUserEmail = true
The email is an HTML Template and the assignement Rules is working: TEST: when I create an email manully within SAlesforce (create new LEad) the email IS send.

yes, the Assignement Rule got a template (See attachment1) and the LEad is assignemed to the correct Queue
(see attachmenet 2). Attechment1 also shows the Criteria