I actually wrote an extension plugin that lets you add a category to emails.
https://github.com/CodeAwhile/wp-sendgrid-categories
You’re not the first person to ask for the feature, so I’ve just submitted a request for this extension to be hosted on WP.org (so that updates are easier). Once it’s been approved, you’ll be able to download it from WP.org, but until then, you can just download it from GitHub.
The “Wp SendGrid Categories” plugin is now on WordPress.org.
http://wordpress.org/extend/plugins/wp-sendgrid-categories/
Closing this thread.
