How to write a salutation and close an email?

Okay, the recent email introduction lesson just left too many questions for me.  Hamshank and I asked a few questions, but a few have been unanswered, or I am unsure about the answers.  Therefore, lets try to settle this here.

Salutations

How to say something similar to these:

1. Hey mate/dude/bro (Are normal Chinese adults likely to use such informal language in emails?)
2. Dear Sir/Madam/Mr. so-and-so/Ms so-and-so (clearly formal, and I know 'dear' should be 亲爱的)
   
3. To whom it may concern (basically, how do we address an email when we don't know who will recieve it?)

Are there any other common ways to address a person that are not analagous to the methods used above?

Closing an email

How to say something similar to these:

1. Yours truly/sincerely, Best regards, etc. (formal) Bodawei suggested 你的真挚的 for yours truly/sincerely, but do Chinese typically use it?  Or is it just a translation that some people use?
2. Later, see ya (very informal)

I think that perhaps the following are good to use when closing a letter, even though they are not direct translations.  Are the following normal?

致 zhì

            礼 lǐ

and...

至此 zhìcǐ

            敬礼 jìnglǐ

Thank you everybody!