Commenting to an Existing Ticket through Email would not Create the User

Steps to Reproduce:

1. Create a Dummy Service Desk Project.
2. Specify the Email Settings and Turn On the Public Sign Up for the Dummy Service Desk Project.
3. Go to JIRA and configure the Outgoing Mail/Notification.
4. Using Email Address A that is not registered yet, sent an email to create the issue and a user on the Service Desk Project.
5. The User will be notified about the issue cretion and get an invitation link.
6. Using Email Address B which also not registered as a user, use the same Subject as the Notification Email Subject that Email Address A received.
7. Then with the same subject and a body, sent an email to the Dummy Service Desk project Mail Server.

Expected Result:

• Like in JIRA, the user will be created and it will make a comment on the existing ticket.

Actual Result:

• The user is not created and the email is rejected.

Notes:

• Have tested in JIRA side with a "Create User" option enabled, the User will be created and a comment will be added on the mentioned ticket.