I believe you will need to set up a cron job to make it automagically check, but I'm not really sure about that in 2.*. The last time I used blog by email was before 1.* happened so my info is a bit out of date ;)

So i just need to set up a cron job for blogs/cron/getmail.php ?

I'm pretty sure that's all you have to do, but it's been a long time since I used that feature and had to beat my head against the wall profusely to figure out how to make cron jobs work. Now it's available via the back office - hm!

it still doesn't work when the cron deamon or someone else is starting getmail.php it seems like b2 won't grant him to post. :-/

it only works when i'm logged in and open getmail.php manually.