Postfix set limit of user mail

[wang <wang@ric.ws>]

HELLO!
	How can i set the limit of user mail at /var/spool/mail
	Because i have some message at th log
	
	to=<webmaster@gogorock.com>, relay=local, delay=1,
	status=bounced
	(cannot access mailbox /var/mail/webmaster for user webmaster.
	error writing message: File too large)
	
	MANY THANKS
	
	wang