We've been using this plugin and had a couple hiccups. I've refactored to remove debug notices, updated the readme to say it's compatible with 3.9 and to match the one you get from the wp.org repo, added a boolean false check on the check for the html header so that if someone passes 'text/html' as a header it still sends as html and added a nonce check to the admin section. Let me know if you see any issues.
We've been using this plugin and had a couple hiccups. I've refactored to remove debug notices, updated the readme to say it's compatible with 3.9 and to match the one you get from the wp.org repo, added a boolean false check on the check for the html header so that if someone passes
'text/html'as a header it still sends as html and added a nonce check to the admin section. Let me know if you see any issues.