The "ERROR: Connection dropped by IMAP server" is because there is no mail in /home/vmail/your_domain.com/lars.
For some reason it is not seeing your user.
Check the /etc/postfix/main.cf file for this line:
virtual_mailbox_base = /home/vmail
This line tells the system where mail should be delivered.
The way it should work is
If that is right, check the Mail database for errors.
In the console do:
(ENTER ROOT PASSWORD)
switch to the mail db
to display all domains
SELECT * FROM domains
to display all users
SELECT * FROM users
if everything is right
then just to be safe do: