✨(mailbox) remove secondary email as required field

The secondary email address is no longer required for all creation
processes and we should not force the user to provide and store an
insecure email address.

src/backend/mailbox_manager/utils/dimail.py

@@ -334,9 +334,6 @@ class DimailAPIClient:
                             last_name=dimail_mailbox["surName"],
                             local_part=address.username,
                             domain=domain,
-                            secondary_email=dimail_mailbox["email"],
-                            # secondary email is mandatory. Unfortunately, dimail doesn't
-                            # store any. We temporarily give current email as secondary email.
                             status=enums.MailboxStatusChoices.ENABLED,
                             password=make_password(None),  # unusable password
                         )
@@ -408,11 +405,18 @@ class DimailAPIClient:
             mailbox.status = enums.MailDomainStatusChoices.ENABLED
             mailbox.save()
 
-            # send confirmation email
-            self.notify_mailbox_creation(
-                recipient=mailbox.secondary_email,
-                mailbox_data=response.json(),
-            )
+            if mailbox.secondary_email:
+                # send confirmation email
+                self.notify_mailbox_creation(
+                    recipient=mailbox.secondary_email,
+                    mailbox_data=response.json(),
+                )
+            else:
+                logger.warning(
+                    "Email notification for %s creation not sent "
+                    "because no secondary email found",
+                    mailbox,
+                )
 
     def check_domain(self, domain):
         """Send a request to dimail to check domain health."""