דירוג 5 מתוך 5 כוכבים

OK :) But why it do not work with RSS-accounts?

דירוג 3 מתוך 5 כוכבים

How can I use it - do not understand?

IMAP only?
Where is it options?
How do it work and when?

Go to Account Settings->Archive settings and choose age of messages to archive. Thunderbird will archive messages automatically after next restart and every 24 hours in the case if you do not close Thunderbird.