This article specifically relates to the Email service's Applets that run when you send emails to firstname.lastname@example.org:
Send IFTTT any email
Send IFTTT an email tagged
The Email service doesn't work for every email domain. If you use an email address with a common domain such as Gmail, iCloud, or Outlook, your Applets should work.
You can change the email address you have connected to IFTTT on the Email service's settings page.