fix: address code review findings

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: lavr

docs/index.rst

@@ -46,6 +46,7 @@ clean, intuitive API.
 - Load messages from URLs, HTML files, directories, ZIP archives, or RFC 822 files
 - Django integration via ``DjangoMessage``
 - SMTP sending with SSL/TLS support
+- Async sending via ``aiosmtplib``
 
 
 .. toctree::