CJ (who works our help desk) received 2 emails within 2 days asking me the same thing.
How did you get an email to send out automatically after someone comments on your blog? Will you share it?
Of course! But before that, thanks to Carrie and Marie for asking – and commenting! I relish all comments and appreciate every single one – except spam of course. Eeewww.
The plugin I use is Comment Relish by Justin Shattuck. It is pretty old and I’m not sure it’s supported anymore but I am running the latest WordPress and it still works at time of writing.
What I like about this is the auto email thanks of course but better, the ability to customize this message.
In fact, this message just reminded me it is probably time to change the message. You can download the plugin from Justin’s site.