If you are looking for a free email subscription service which will associate with your RSS feed and will send emails to subscribers whenever you have new contents on your blog or website, I recommend you try Google feedburner Email Subscriptions service.
Follow these simple steps below to get your own email subscription widget for your blog/site:
1. Login to http://feedburner.google.com/ with your Google Account
2. Choose a Feed you would like to setup the email subscription service, if you don’t have any feed, you will need to burn your feed first.
3. Click the Publicize tab as picture below:
4. Click on the link “Email Subscriptions” from the left panel:
5. On Email Subscriptions page, click on the “Active” button to make sure you really want to active this service.
6. Now you should see a html code like below:[text] <form style="border:1px solid #ccc;padding:3px;text-align:center;" action="http://feedburner.google.com/fb/a/mailverify" method="post" target="popupwindow" onsubmit="window.open(‘http://feedburner.google.com/fb/a/mailverify?uri=4RapidDevelopment’, ‘popupwindow’, ‘scrollbars=yes,width=550,height=520’);return true"><p>Enter your email address:</p><p><input type="text" style="width:140px" name="email"/></p><input type="hidden" value="4RapidDevelopment" name="uri"/><input type="hidden" name="loc" value="en_US"/><input type="submit" value="Subscribe" /><p>Delivered by <a href="http://feedburner.google.com" target="_blank">FeedBurner</a></p></form>
Just copy that code and place somewhere on your blog/website and then readers can subscribe to receive daily email with your newest content.
Preview for the widget looks like the picture below which is captured from my blog
Note: Under the “Email Subscriptions” link, you can change HTML Email Appearance in Email Branding tab, Email from address, Subject and Confirmation Email Body in Communication Preferences tab and much much more there.