Stop Gmail Grouping Your Site's Emails Into Threads
Adds a unique reference header to every email so Gmail shows each notification separately instead of bundling emails with the same subject into one long conversation.
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.