First time visitors are important to any site. With this plugin, you can automatically send a "thank you" email to those who comment on your blog for the first time. Additionally, it helps keep your visitor engaged by reminding them to check back at that link for any further information/comments. http://wordpress.org/extend/plugins/thank-me-later/
Our Blog About Blogging
Tips and Tales from Decades of Internet Marketing, Writing, and Blogging.
If you have a blog and allow comments, you'll get comment spam. On this page, WordPress talks about how to combat comment spam. http://codex.wordpress.org/Combating_Comment_Spam