Write SMTP Conversation to the Debug Log
Records the conversation between WordPress and your SMTP server in the PHP error log while you troubleshoot, with passwords and login tokens blanked out.
Snippet Library
Email snippets for WordPress
Snippets for the emails WordPress sends: change the sender name and address, add a Reply-To header, send HTML email and turn off notifications you do not need. For site owners who want their messages to arrive and look right.