For this bug i activated mailing in my playground. I also set all email adresses to some dummy values so that actual users didnt get interruped by testing.

I observed in Email Registrents 3 errors.
1.)
When ever i try to send a new Email to the Registrents I get the following error message regardless if there are some or not : There are no records that match the selections you have made.
That is not correct he also found some and he generated the list of emails witch i can see here:
http://playground.inseln-der-macht.de/administrator/index.php?option=com_dtregister&task=list&controller=massemail < = clicking on view Emails on the right

2.)
The found Registrants or better said their Emails where generated, but not send automaticlly. so all are in status failed. I can see them here and send them manually one by one.
http://playground.inseln-der-macht.de/administrator/index.php?option=com_dtregister&task=list&controller=massemail < = clicking on view Emails on the right

3.
When a User buys to tickets he only get one mail. You can test it easy. By modifing any record, so that the modified Record has the same email then a other one from the same event. No create a "Mass mail" with http://playground.inseln-der-macht.de/administrator/index.php?option=com_dtregister&controller=registrantemail <= by selecting what ever event you modified the record.

click on send email
go back to http://playground.inseln-der-macht.de/administrator/index.php?option=com_dtregister&controller=massemail and click right side on the view emails button....

now you will see for your modified record there is only one email generated..
This is not correct! Think about a Family Father buys 2 ticket one for him and one for his child. I like to send out both tickets to the email in the record, but with the data of each Record. so 2 individual emails it should be. Now i get one email with the later records data and the first one is not rendered.