Email Delivery Check in Site Health
Adds a test to Tools > Site Health that warns when WordPress sends mail with plain PHP mail() instead of SMTP or an API, and when an email has failed recently.
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.