If you’re talking about HTML emails that are formatted and include images etc. It is possible to do in Sparkle, but the email must be hosted on a server for it to work.
Essentially, it works the same way as sending a webpage by email. In Safari you have the option of emailing a web page (as opposed to emailing a link in other browsers). This means you can create an email page containing images links and anything else then upload it to a folder on your server as a complete web page, along with its folders and files. You then visit the URL of your email page in Safari and use the share option in Safari’s file menu. This will open the web page in Apple pages so that you can email it to one or more recipients.
Here is an example of a web page as seen inside Apple Mail. You’ll notice that it automatically includes a link to the actual web page just in case a recipient cannot see the formatted page.