Due to the way email is delivered in the school, if you choose to use mdbox or maildir, you will need to take special care with .forward or .procmailrc configurations. The advanced mailbox formats require that dovecot (the imap server) be responsible for final delivery. This means that your configurations must be aware of dovecot.
For .forward that means using an #Exim filer command at the beginning of your .forward.
#Exim filter unseen deliver email@example.com
DELIVER="/usr/bin/deliver" LOGFILE="$HOME/.procmail.log" :0 * ^From priya@* | $DELIVER -d $LOGNAME -m Priya :0 w | $DELIVER -d $LOGNAME