How often and how soon

I have been reading a lot about e-mail marketing and have a question I want cleared up. Everyone says get subscribers the same way through an opt in page.

Then in their auto responder the first e-mail that is sent out is a thank you page. After that some people say start sending sales pitches right off the bat and others say you need to send out information letters because you want to gain the readers trust before you send them content with a sales pitch in it.

My question is how do you know how many non sales letters or notes, whatever you want to call them should be sent out before you send out the first article that includes a sales pitch.

Also how often should someone send out e-mails, 2, 3 times a week or more, does it depend on the market you are in.
Also how often do you send out a sales pitch compared to just an info e-mail.

So many things I have read talks about trust and getting the person reading your e-mails to feel like you are almost a friend and trust what you are saying is true. Then when an e-mail is sent out recommending buying something they might trust what you are saying and buy what you are talking about.