Variables from Email template are not populated when related to Custom module

I created a custom module “Inschrijvingen” (enrollments) and would like to send an email with as contents a related email template. Unfortunately the defined variable (name) in the email template does not get populated in the received sent mail.
Did I forget a step / some steps?

Thanks in beforehand!

Steps:

  • created a many to many relationship with Email module
  • added the custom module to the “Related to” dropdown via the Dropdown Editor

Sending the mail:

  • click on the mail icon to the right of the “Inschrijving”
  • applied a test mail template which shows the name field of the custom module
  • send the mail