🐛(backend) fix dimail call despite mailbox creation failure on our side

When we try to create a duplicate email, a request
to dimail is sent despite a reject on our side.
To solve this issue, we call mailbox creation first
to benefit from validation of our Django model.

Mailbox creation try was called too late after dimail call.
So in attempt to create a duplicated email a request
to dimail was sent despite a failure in our side.

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to
 
 ### Fixed
 
+- 🐛(backend) fix dimail call despite mailbox creation failure on our side
 - 🧑‍💻(user) fix the User.language infinite migration #611
 
 ## [1.9.1] - 2024-12-18