2 files changed, 24 insertions, 2 deletions

diff --git a/src/mailman/rest/docs/users.txt b/src/mailman/rest/docs/users.txt
index fcdbdd952..3dfa29bc8 100644
--- a/src/mailman/rest/docs/users.txt
+++ b/src/mailman/rest/docs/users.txt
@@ -82,3 +82,12 @@ It is of course an error to access a non-existent user id.
     ...
     HTTPError: HTTP Error 404: 404 Not Found
 
+Because email addresses just have an ``@`` sign in then, there's no confusing
+them with user ids.  Thus, a user can be retrieved via its email address.
+
+    >>> dump_json('http://localhost:9001/3.0/users/bart@example.com')
+    created_on: 2005-08-01T07:49:23
+    http_etag: "..."
+    password: None
+    real_name: Bart Person
+    user_id: 2
diff --git a/src/mailman/rest/users.py b/src/mailman/rest/users.py
index b8972f3f5..9a00cecd2 100644
--- a/src/mailman/rest/users.py
+++ b/src/mailman/rest/users.py
@@ -95,8 +95,21 @@ class AllUsers(_UserBase):
 class AUser(_UserBase):
     """A user."""
 
-    def __init__(self, user_id):
-        self._user = getUtility(IUserManager).get_user_by_id(user_id)
+    def __init__(self, user_identifier):
+        """Get a user by various type of identifiers.
+
+        :param user_identifier: The identifier used to retrieve the user.  The
+            identifier may either be an integer user-id, or an email address
+            controlled by the user.  The type of identifier is auto-detected
+            by looking for an `@` symbol, in which case it's taken as an email
+            address, otherwise it's assumed to be an integer.
+        :type user_identifier: str
+        """
+        user_manager = getUtility(IUserManager)
+        if '@' in user_identifier:
+            self._user = user_manager.get_user(user_identifier)
+        else:
+            self._user = user_manager.get_user_by_id(user_identifier)
 
     @resource.GET()
     def user(self, request):