diff --git a/plinth/modules/email_server/aliases/__init__.py b/plinth/modules/email_server/aliases/__init__.py
index 82de702b5..760ecb0cc 100644
--- a/plinth/modules/email_server/aliases/__init__.py
+++ b/plinth/modules/email_server/aliases/__init__.py
@@ -125,7 +125,8 @@ def schedule_hash_update():
                 alias = models.Alias(**row)
                 key = alias.email_name.encode('ascii') + b'\0'
                 if alias.enabled:
-                    value = str(alias.uid_number).encode('ascii') + b'\0'
+                    value = str(alias.uid_number).encode('ascii')
+                    value +=  b'@localhost\0'
                 else:
                     value = b'/dev/null\0'
                 db[key] = value
diff --git a/plinth/modules/email_server/data/etc/postfix/freedombox-username-to-uid-number.cf b/plinth/modules/email_server/data/etc/postfix/freedombox-username-to-uid-number.cf
index c8919becf..70a59bcee 100644
--- a/plinth/modules/email_server/data/etc/postfix/freedombox-username-to-uid-number.cf
+++ b/plinth/modules/email_server/data/etc/postfix/freedombox-username-to-uid-number.cf
@@ -7,3 +7,4 @@ server_host = ldap://127.0.0.1
 search_base = dc=thisbox
 query_filter = (&(objectClass=posixAccount)(uid=%s))
 result_attribute = uidNumber
+result_format = %s@localhost