Describe the bug
When inviting a Non Existing Participant to a Conference. This Non Existing Participant never receive the invitation mail.

To Reproduce
Steps to reproduce the behavior:

1. Create a Conference and publish it
2. Create a Registration Type
3. On the Invite page, select Non Existing Participant and fill the form
4. The status said that the invite is sent but no email in the letter_opener is received for that Conference invitation.

Expected behavior
The Non Existing Participant should receive an invite mail in the letter_opener for instance.

Screenshots
When filling the invite form:

To see the status:

Extra data (please complete the following information):

• Device OS: Windows 10
• Device: letter_opener
• Browser: Chrome
• Decidim Version: 0.25.2 and 0.26 (try.decidim.org)