Easydiscuss digest : how to ?

Hello,

Thanks for the new Digest feature on ED4, i would like to know how this function is working in some questions :

1. all members are subscribed by default to receive digests ? existed members too (after upgrade) ?
2. the digests are sent like notifications ?
3. when the mails are sent ? Ca we choose the time ?
4. How disable this feature ?

Thanks