I loved using dmail because it was easy to send out emails that would disappear after sending them, but could be easily sent back so you didn't lose any data if people didn't want your message anymore. Sometimes there were problems with messages not being sent or received at all when we first set up our server (maybe due to traffic?), but once everything got figured out they worked very well for us. We used this service as an experiment while learning more about how different providers work together in order to get large amounts of information from customers quickly without having issues getting customer feedback afterwards.