Hi Stefan,
Thank you for your message.
Of course you can delete it form queue. You can do it by passing the Email ID. The ID is the column ItemID you can found in Table CMS_Email. Once you have the E-mail ID of email you want to delete you can simply call:
CMS.EmailEngine.EmailHelper.Queue.Delete(1);
Where 1 is the value EmailID.
E-mail provider does not hold this information, you should find the e-mail information in the EmailInfo object.
Kind regards,
Richard Sustek