For the automatic processing, you need to use LR's email dialog.
Otherwise, you need to manually export your images (where you control all the export properties), then open your email client, create a new message and manually attach your exported images.
Well, unfortunately that's no help at all. In Aperture I click the email button or option-e and it drops the photo into my email client where I can use a dropdown for what size I want to send. Of course I have all my contacts connected to my email client so no problem there. Automatic processing with no contact list is useless. Am I missing something here?