In your title you say "but i won't automaticaly download even the old emails" but in the body your say " thunderbird automaticaly download from server all old emails"

Which do you mean please?

after set the account,thunderbird automaticaly dwonload the old emails and i dont want that . what cand i do ?

An email client is designed to show you email messages that have arrived in your account and are waiting on the server. It can't know which messages you want to see and which you don't.

Gmail offer a "recent" mode which offers you just 'new' messages but this is only relevant with a POP-connected account.

Is your account POP or IMAP? Why do you keep on the server old messages that you don't want to see?

my question it very simple ...i repeat again....i have one computer with thunderibird instaled and emails arrived, ok ? and i instal thunderibird on another computer where i set my existent account.When i made that,all the old emails autmaticaly download on the new computer ! its there tehnical posibility to do NOT automat import the old emails in the new set account on my new computer? i have an imap mail . thank

In simple terms, no. The whole point of IMAP is that you see the same set of folders and the messages in them regardless of which device or computer you use. You have seamless access to all of your email, always.

Maybe you could organise your messages into various folders and selectively subscribe in Thunderbird only to the required folders?

I UNDERSTAND...thank you