chore: Better example config

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

example_configs/stalwart.md

@@ -48,3 +48,13 @@ To integrate with LLDAP,
       allow-invalid-certs = true
       enable = false
 ```
+
+## Email alias
+If you want to enable [email aliases](https://stalw.art/docs/mta/inbound/rcpt/#catch-all-addresses), you have to create a new *User-defined attribute* under *User schema* of type string. Currently, LLDAP doesn't support multi-value filters. If you want multiple aliases, you will have to create multiple attributes (`mailAlias1`, `mailAlias2`, ..., `mailAliasN`), where `N` is the maximum number of aliases an account will have.
+
+You also need to change your ldap filter for emails.
+```toml
+[directory.ldap.filter]
+# Add one clause per alias attribute you created (example: mailAlias1..mailAlias3)
+email = "(&(objectclass=person)(|(mail=?)(mailAlias1=?)(mailAlias2=?)(mailAlias3=?)))"
+```