Very good work on this task
Some small remarks:
- You don’t need
<address>as an address is italic by default
<p>is not allowed inside
<time>. So the first date should look like:
<p class="sender-column"><time datetime="2016-01-20">20 January 2016</time></p>
- Similar than the point above: On the last line you have a
<strong><em><p>this should be
<p><strong><em>to create a valid structure.
I hope that helps!
Have a nice day!
PS: On your Discourse account your email address ended up in the optional name field and is now visible for everyone reading your posts. I recommend removing it from there.