S Hetjens

This plug-in redirects requests to the main or comment feeds, and only theses two, to Feedburner or a similar service. In comparision to the original Feedsmith-plug-in is has three advantages:
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It redirects only the two main feeds of the blog and not all. The category, tag and author feeds are still accessible
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If you need access to the original blog feed you can add the URL parameter “noredirect” (i.e. /feed/?noredirect) to your feed address and it will not forward your request.
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The Plugin is more integrated into the administration interface. It adds its settings to the default “reading” settings pages and do not create an own page.
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Hetjens Feed Redirect

This plug-in redirect reqests to the main or comment feed of the blog to Feedburner or a similar service.

Md Abul Bashar

Just use Feedburner Email Subscriber service on your website sitebar widget.
Full <a href="http://www.codingbank.com/item/wp-feedburner-email-subscriber-wordpress-plugin/" rel="nofollow ugc">Documentations</a>
You can watch this videe 
https://www.youtube.com/watch?v=lqQnR_21UvQ

WP Feedburner Email Subscriber

Does the job

Just use Feedburner Email Subscriber service on your website sitebar widget..

Hetjens Feed Redirect vs WP Feedburner Email Subscriber