If you publish on your blog 10 posts a day for instance, Jetpack is sending 10 e-mails a day. It may be intrusive for subscribers. How can we merge all posts in one daily or weekly e-mail digest? Like feedburner subscription for example.
There isn’t a way to set that for your followers. Jetpack will respect the default WordPress.com subscription settings, if the follower’s e-mail address is associated to a WordPress.com account, but there isn’t an option for the site owner to control frequency.