Quote Originally Posted by Antonio1986 View Post
"Прошло достаточно много времени как мы общались ..."
The expression in English is: It passed a lot of time since the time we communicated (implied: for a last time).
Is the word kak playing the role of since?
Yes, it's rather colloquial though and you're missing a comma before как, just saying

Quote Originally Posted by Antonio1986 View Post
Also I want to write: It has passed a lot of time since the first e-mail I sent you (It is implied that this is the second e-mail):
Прошло достаточно много времени с моего первого сообщения
I pass the meaning I want?
That actually depends. You didn't really specified what type of "сообщение" you mean, so it can be ambiguous. If you truly want to express the meaning distinctively I'd recommend saying it like this:

Прошло много времени с того момента, как я отправил тебе (вам) электронное письмо.

Kind of like that, variations are possible as usual of course

Hope it helps