We create a email link of current post:

<?php 

$email_link = 'subject='.urlencode(get_the_title()) .'&body='. urlencode(esc_url(get_permalink()));
?>

Add the button to html

<!--social share-->


<div class="prop_social_single">

<a href="https://www.facebook.com/sharer.php?u=<?php the_permalink(); ?>&amp;t=<?php echo urlencode(get_the_title()); ?>" target="_blank" class="share_facebook"><i class="fa fa-facebook"></i></a>
<a href="https://twitter.com/intent/tweet?text=<?php echo urlencode(get_the_title() .' '. esc_url(get_permalink())); ?>" class="share_tweet" target="_blank"><i class="fa fa-twitter"></i></a>
<a href="https://pinterest.com/pin/create/button/?url=<?php the_permalink(); ?>&amp;media=<?php echo esc_url($pinterest[0]);?>&amp;description=<?php echo urlencode(get_the_title()); ?>" target="_blank" class="share_pinterest"> <i class="fa fa-pinterest-p"></i> </a>
<a href="mailto:email@email.com?<?php echo trim(esc_html($email_link));?>" class="social_email"> <i class="fa fa-envelope"></i></a>
<a href="https://www.linkedin.com/sharing/share-offsite/?url=<?php the_permalink(); ?>&amp;media=<?php echo esc_url($pinterest[0]);?>&amp;description=<?php echo urlencode(get_the_title()); ?>" target="_blank"> <i class="fa fa-linkedin"></i></a>

</div>