Hi there,
If you don't insert the images into your post, then they cannot be sent out to your subscribers as they are not part of the post content. However, one of Jetpack's great features, Photon, automatically resizes your images so they don’t exceed the width supported by your theme.
http://jetpack.me/support/photon/
You should be able to enable Photon in Jetpack and use it to manage your post's images. Please let me know if you have any problems or questions.
Best!