auth between postfix and dovecot?

[ミユナ (alice)]

hello experts,

I have installed postfix and dovecot in the same machine.

Their configure looks as:

service lmtp {
    unix_listener /var/spool/postfix/private/dovecot-lmtp {
      mode = 0600
      user = postfix
      group = postfix
    }

unix_listener /var/spool/postfix/private/auth {
    mode = 0666
    user = postfix
    group = postfix
  }

  auth_mechanisms = plain login

  !include auth-passwdfile.conf.ext



my question is:

when postfix talks to dovecot, does it require user's username/password 
for authentication? or this communication just goes without authentication?

I asked this, b/c my webmail send mail from localhost has been going 
without authentication to postifx. so i am not sure if postfix talks to 
dovecot without requiring auth too.


Thanks
alice