Adding user to an Event by API - no confirm. email

User does not get a confirmation email. Even all email-option are marked.

Here is my  add function and reqest:

public void AddUserToMeeting(int scoId, String mail, MeetingRoles role)

        {

            String principal_id = GetPrincipalIdByEmail(mail);

            Request("permissions-update",

                    "principal-id=" + principal_id +

                    "&acl-id=" + scoId +

                    "&permission-id=" + GetRole((int)role) +

                    "&send-email=true" );

        }