Mails composed from Dragonfly currently have a number of issues, viz.:

Content-Transfer-Encoding: 7bit
Content-Type: multipart/alternative; boundary="===============0649628103=="

--===============0649628103==
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit

This is a test e-mail<br><br>Let's see if we can send it.<br>

--===============0649628103==
MIME-Version: 1.0
Content-Type: text/html; charset="us-ascii"
Content-Transfer-Encoding: 7bit

This is a test e-mail<br><br>Let's see if we can send it.<br>

--===============0649628103==--

There are a few things wrong with this:

• the test/plain content has encoded HTML,
• charsets are "us-ascii" - we should be UTF-8 (this may necessitate work to ensure 8-bit+ values get correctly encoded)
• we should be sending 8bit mail, not 7bit. If the receiving server cannot handle 8bit(!), that's SMTP's problem.

It's likely most of this is Python-side.