[NEW] account_move_protect_reset_to_draft

account_move_protect_reset_to_draft/models/__init__.py

@@ -0,0 +1 @@
+from . import account_move

account_move_protect_reset_to_draft/models/account_move.py

@@ -0,0 +1,15 @@
+from odoo import models, api, _, fields
+from odoo.exceptions import UserError
+
+class AccountMove(models.Model):
+    _inherit = 'account.move'
+
+    sent_by_email = fields.Boolean()
+    
+    def button_draft(self):
+        res = super(AccountMove, self).button_draft()
+        if self.sent_by_email:
+            raise UserError(_(
+                "You cannot reset to draft this invoice because it has been sent by email."
+            ))
+        return res