If the constituent's preferred locale is configured for "en_US" but the site only uses "en_CA" and "fr_CA", then any constituents configured for "en_US" could receive a blank email. This is probably because the "en_US" version of the email has not been configured. This also occurs if the constituent preferred locale is completely blank.

In order to fix this issue, you need to assign an accepted preferred locale to each constituent. The steps to do so are listed below.
  1. Create a Query and add the Field Type: Biographical Information and the Field: Preferred Locale.
  2. You'll want to add 2 clauses, "Preferred Locale equals en_US" or "Preferred Locale is blank."
  3. Now, you'll need to create a group from the query results and do a Mail Merge.
  4. Be sure to include Biographical Information/Preferred Locale in the mail merge as well as any primary key (Email/Constituent ID/Member ID) to identify the constituent.
  5. Now change the Preferred Locale column to use any of the supported locales for your site, such as en_CA.
  6. Use this mail merge to do a Custom Constituent Import which will change the preferred locale for all of the records.