diff --git a/mail_environment/migrations/18.0.1.0.1/post-migration.py b/mail_environment/migrations/18.0.1.0.1/post-migration.py
new file mode 100644
index 000000000..523be970a
--- /dev/null
+++ b/mail_environment/migrations/18.0.1.0.1/post-migration.py
@@ -0,0 +1,9 @@
+# Copyright 2026 ACSONE SA/NV
+# License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl).
+
+from openupgradelib import openupgrade
+
+
+@openupgrade.migrate()
+def migrate(env, version):
+    env["ir.mail_server"]._preserve_not_env_managed_data(["smtp_authentication"])
diff --git a/server_environment/models/server_env_mixin.py b/server_environment/models/server_env_mixin.py
index 65f0d029a..f58f3ffa8 100644
--- a/server_environment/models/server_env_mixin.py
+++ b/server_environment/models/server_env_mixin.py
@@ -428,3 +428,31 @@ def _setup_base(self):
             self._server_env_transform_field_to_read_from_env(field)
             self._server_env_add_is_editable_field(field)
         return
+
+    @api.model
+    def _preserve_not_env_managed_data(self, field_name_list):
+        """
+        Helper function typically used for hooks and migration scripts.
+        Restores database values for fields transitioning to 'server env managed'.
+
+        When a field is defined as managed by the server environment, Odoo
+        ignores the value stored in the database, prioritizing the environment
+        configuration instead. If no environment configuration exists, the field
+        may effectively lose its previous value.
+
+        This method forces to 'persist' these values if they are not
+        explicitly overridden by the current environment configuration.
+        """
+        self.env.cr.execute(f"SELECT * FROM {self._table}")
+        for row in self.env.cr.dictfetchall():
+            record = (
+                self.env[self._name]
+                .with_context(active_test=False)
+                .search([("id", "=", row["id"])])
+            )
+            if record:
+                record_values = {}
+                for field_name in field_name_list:
+                    if field_name in row:
+                        record_values[field_name] = row[field_name]
+                record.update(record_values)