diff --git a/exchangelib/folders/base.py b/exchangelib/folders/base.py
index a8b5647a..d9af1029 100644
--- a/exchangelib/folders/base.py
+++ b/exchangelib/folders/base.py
@@ -96,7 +96,8 @@ def __init__(self, **kwargs):
         self.item_sync_state = kwargs.pop("item_sync_state", None)
         self.folder_sync_state = kwargs.pop("folder_sync_state", None)
         super().__init__(**kwargs)
-        if self._distinguished_id and self.account:
+        if self._distinguished_id and not self._distinguished_id.mailbox and self.account:
+            # Ensure that distinguished IDs have a mailbox, but don't override a custom mailbox (e.g. shared folders)
             self._distinguished_id.mailbox = Mailbox(email_address=self.account.primary_smtp_address)
 
     @property
diff --git a/tests/test_folder.py b/tests/test_folder.py
index 13556afa..dde0c224 100644
--- a/tests/test_folder.py
+++ b/tests/test_folder.py
@@ -500,6 +500,18 @@ def test_get_folders(self):
                 ).get_folders()
             )
 
+    def test_shared_folders(self):
+        # Test that the custom 'email_address' is not overwritten. The test account does not have access to any shared
+        # accounts, so we can't expand the test to actual queries.
+        shared_folder = Folder(
+            root=self.account.root,
+            _distinguished_id=DistinguishedFolderId(
+                id=Inbox.DISTINGUISHED_FOLDER_ID,
+                mailbox=Mailbox(email_address="foo@example.com"),
+            ),
+        )
+        self.assertEqual(shared_folder._distinguished_id.mailbox.email_address, "foo@example.com")
+
     def test_folder_grouping(self):
         # If you get errors here, you probably need to fill out [folder class].LOCALIZED_NAMES for your locale.
         for f in self.account.root.walk():