The plugin did work and then it stopped. I checked for plugin conflicts and found none. I installed wp mail and successfully sent mail from the site. I believe I have isolated the problem to the plugin.
Are there any other tests I can do or is there a working solution or a fix?
I am having the exact same problem where the email is not sending but it seems to be working when I use the WP mail. I have requested help from the author but have not heard anything back as of yet.