In smrtDialer, only the answered calls get a disposition status. If the calls are not answered by a human or a recording/voicemail, they receive a "no disposition" status.
If you find this happening frequently in your campaigns, there are two potential root causes:
Poor List Quality
How confident are you in the quality of your list? Campaign results with a high percentage of no disposition status are typical of cold lead lists that haven't been thoroughly scrubbed. It could be the list itself that is leading to these results.
Ring Timeout is Insufficient
Another option is to consider whether your Ring Timeout is too short. Ring Timeout is a setting within the campaign Call Engine tab that determines how long the system will wait to determine if the call is answered/voicemail/unanswered.
The default in smrtDialer is 20 seconds, which is approximately 3 to 4 rings in the U.S. Perhaps the target audience has their voicemail set to pick up after 5 or 6 rings. You can try increasing this setting and see if it results in more voicemail drops.
If you see these same results in multiple campaigns, with different lists, let us know. We will happily take another look behind the scenes to see if we can pinpoint any other issues with your smrtDialer campaigns.