How can I send html email notifications with entityforms? There must be a way to do this, but I'm having trouble turning it up.  Has anyone successfully sent HTML email notifications following an entityform submission?
Here some more detailed guidance on how to solve this:

HTML EMAILS

You will need to download and set up Mime Mail.

The latest version of Entity Form (currently 7.x-2.0-rc1) comes with it's own preconfigured rules. You'll need the Entity Rules module for these. You can clone or edit these.

Alternatively you can set up your own fresh rules in the 'normal' way by using the 'After saving a new entityform submission' event.

Whichever method you go for you will need to add the 'Send HTML e-mail' element to the Actions stage of the rule (you can remove the existing actions if you cloned the packaged entity rules).

You can configure KEY, TO, CC, BCC, SENDER NAME, SENDER E-MAIL ADDRESS, REPLY E-MAIL ADDRESS, SUBJECT, BODY, PLAIN TEXT BODY, ATTACHMENTS, LANGUAGE.

EMAIL FILE ATTACHMENTS:

A lot of people have trouble getting file attachments to work with Entity Forms. 

To do this:

Edit the action and within the attachments section you can add a file path token, e.g.

[entity:THE_FILE_FIELD_NAME:file:path]

Check the Replacement Patterns for the field name and make sure you use 'file:path' as above and you will get an attachment on the HTML email.

Other file tokens include:

[entity:THE_FILE_FIELD_NAME:file]

[entity:THE_FILE_FIELD_NAME:file:url]

[entity:THE_FILE_FIELD_NAME:file:size]


You may wish to use these in the email body for example.

Here is a list of file tokens. There are other useful tokens listed on there too.