If put 3 emails into stream, will the cast send out all 3 emails at each cast date? Or will it send email 1 on the first cast date, email 2 on the second cast date and email 3 on third cast date?
The stream will send each lead the first piece of content they have never received. If all of your leads have never received any of the emails, then it will only send the first. If some have received the first, and some the second, then it would send each lead the next email in line. It's possible that it could send all three in one cast, but never to a single lead.
In general, the idea is that each lead will get 1 email per Cast in the order you set the emails in the Stream, top to bottom. Plus whatever John said.
See if this makes sense:
Cast schedule - every Monday.
On Sunday 1/1 you add 5 records. On Monday 1/2 they all receive Email 1
On Sunday 1/6 you add 6 records. On Monday 1/7 the first group of 5 will receive Email 2, the second group of 6 you added will receive Email 1.
On Sunday 1/13 you add 4 records. On Monday 1/14the first group of 5 will receive Email 3, the second group of 6 will receive Email 2 and the last group of 4 will receive Email 1.