• Is the destination a connection to another service?: Check to ensure the login credentials for your destination are up-to-date in the ProntoForms system.
• Is your destination service down?: Check to ensure the service your data is being sent to is functional by using your favorite search engine to search, "Is [destination] down?" For example, search, "Is Dropbox down?" in Google.
• Does your destination have a valid recipient?: Check to make sure that your destination has either a valid email in the "Other Addresses to Include" section or that the form label question, which may have a user inputted email, is added to the "Form Labels to Extract" section of the Email Data Destination Details of the data destination.
• Is you Dispatch Destination pointing to the proper username?: If you are using a dispatch destination, be sure that the user's proper username is being pulled from the form.
• Does your Email Destination have a Filter Rule?: If your destination has a filter applied and the inputted expression is not matched then the destination will not go through.

If that doesn't work...