auth between postfix and dovecot?

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