For Default Blogger Templates:If you are using default blogger templates provided by blogger.com, then you don’t have to worry a lot. In order to display the “Email Post to a Friend” button, you just need to enable a function from settings. Go to Blogger >> Layout >> Blog Posts >> Edit >> Then, on the window that pops up, scroll down and check the box for "Show Email Post Links.".
For Custom Blogger Templates:First and foremost, login into your Blogger Account. Once logged in, go to Your Blog >> Template >> Edit HTML and search for the <data:post.body/> Tag. After finding the post.body tag, just below it past the following piece of coding (Mostly, there are more than one <data:post.body/> tags so be sure you paste the following code after all of them).
<!-- email post links -->
<a expr:href='data:post.emailPostUrl' expr:title='data:top.emailPostMsg'>
Email this Post to a Friend
Whenever a reader will click on the "Send Email" link, he will be redirected to blogger.com where he can enter upto 10 email address separated by a comma. Along with the post content, he can also write a small message to his friend. However, this feature is not to be used for advertising or excessive self-promotion.