change dovecot mbox localtion

hi, i use: dovecot 1.2.7, sendmail and unbuntu to serve my mail service. recent my disk space is not enough, so i want to mange my mail in two ways:

*1. change the mail location:* i use: mail_location = mbox:/var/mail:INBOX=/var/mail/%u when i changed it to mail_location = mbox:/home/mail:INBOX=/home/mail/%u but the mail still write to the old path

*2. limit the mail file size* i want the mail file reduce when it reach to 100MB

how can i config dovecot/sendmail to do in last 2 ways?

thank you all:)