Displays the comment author's email address, not linked. An email address must be provided if "User must fill out name and email" is enabled under Discussion Options.
Use get_comment_author_email to retrieve the value.
<?php comment_author_email( $comment_ID ); ?>
<a href="mailto:<?php comment_author_email(); ?>">contact <?php comment_author(); ?></a>
(Note: Displaying email addresses is not recommended, as email spammers could collect them from your site.)
apply_filters() Calls 'author_email' hook on the author email.