From Jetpack…
Thanks for contacting us. I can reproduce this problem on my test site. The shortcode is not supported by Jetpack which means it should appear as plain text in the email. This is not happening at all and instead the shortcode is completely removed. I’m not sure what’s going wrong so I’ve submitted an issue for our developers to take a look at this here:
It appears that JetPack is providing that functionality. I’m not too worried about sending out emails with HTML as most modern email readers should support that. I guess I’ll have to bug someone else about this :-).
Thanks so much for your quick reply. I’ll consider this closed for now.