Add Start-Event, MailTask end End-Event
Connect all three together (see step1.png)
Move connection between Start-Event and MailTask to ServiceTask by dragging the connection point from MailTask to ServiceTask
Move connection between MailTask en End-Event to ServiceTask by dragging the connection point from MailTask to ServiceTask
Delete MailTask by clicking on it and pressing the delete button
All moved connections will color as a red dotted line.
The diagram also gives other failures