Barry Ceelen

Note: Requires the <a href="https://wordpress.org/plugins/post-by-email/" rel="ugc">Post By Email</a> plugin.
The plugin filters the post content after a post has been created via the <a href="https://wordpress.org/plugins/post-by-email/" rel="ugc">Post By Email</a> plugin. 
If the post content contains only a URL it automatically assigns the ‘link’ <a href="https://codex.wordpress.org/Post_Formats" rel="nofollow ugc">post format</a> to the post and wraps the URL in a link tag.
<h4>Github</h4>
Fork me on <a href="https://github.com/barryceelen/wp-post-by-email-links" rel="nofollow ugc">Github</a>.

Post By Email Links

Create new posts with the 'link' post format by sending an email with a URL or link as the body.

Lucy Tomas

This plugin will transform you WordPress blog into a LinkBlog adding the option to insert an external link to your post.
<ul>
<li>The plugin will override your post permalink by default and replace it with the added external link if it exists.</li>
<li>Option to disable this default behaviour, to let you insert the external link manually. Examples are provided in the settings page of the plugin.</li>
</ul>

LinkBlog by Lucy

Transforms your WordPress blog into a LinkBlog

Post By Email Links vs LinkBlog by Lucy