Assuming this page belongs to an agent:
<p>
<i class="fa fa-envelope-o"></i>
<span style="font-size:11px"><?php echo get_the_author_meta( 'user_email' ); ?></span>
</p>
Assuming this page does not belong to the agent, but the email is stored in the page’s custom field named, for example, agent_email:
<p>
<i class="fa fa-envelope-o"></i>
<span style="font-size:11px"><?php echo get_post_meta( get_the_ID(), 'agent_email', true ); ?></span>
</p>