[Dovecot] Postfix LDA vs the Dovecot LDA + other quetions

[Linux Advocate]

> >>> my  /home/vmail/ directories are owned by postfix. do i then need to make
> >> vmail a member of the group?
> >> 
> >> You could just execute Dovecot LDA using postfix user.
> >> 
> > 
> > Therefore, ( copied from dovecot wiki, http://wiki.dovecot.org/LDA/Postfix )
> > 
> > 
> > dovecot   unix  -       n       n       -       -       pipe
> >  flags=DRhu user=vmail:vmail argv=/usr/local/libexec/dovecot/deliver -f 
> ${sender} -d ${recipient}
> > 
> > 
> > I could change the user=vmail:vmail to postfix:postfix ?
> 
> 
> I just heard that Postfix doesn't allow you to do that (as you would have 
> noticed too). So just use vmail.

Ok. but its amazing that dovecot can deliver as vmail, a user who doesnt exist.....how does it accomplish this? 

[root at fwgw vmail]# ls -l

drwx------ 6 postfix postfix 4096 Feb 23 18:25 mesara.biz

Do i need to changes the permissions on the above?