Betygsatt 5 utav 5 stjärnor

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

Betygsatt 3 utav 5 stjärnor

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.