By using this WordPress plugin you can send welcome emails automatically to your blog commentators. The way it works is: When a user places a comment it goes in to the moderation queue and when you approve it, a welcome email is automatically sent to the commentator. This welcome email is sent only once to the first time commentator. So, when the same commentator again comments on one of your posts, this email will not be sent. In the Welcome email you can include a email newsletter sign up form for your commentators to sign up for your blog. However, you need to make sure that you clearly mention your blog name and the post title so that the commentators can remember your post. This is strictly according to proper email marketing guidelines. The idea behind sending the welcome email only once is according to the double opt-in procedures.
Here are the features of this plugin:
1) Edit welcome email: You have the option to edit the subject and the message of the Welcome email which would be sent to your commentators.
2) Tags: There are various tags available which you can use in your Welcome email. For Example, you can use the tag %author_name% for adding the post author name in the Welcome email. Other tags include post author email, commentator name, commentator email, commentator website, link to blog post and your blog URL.