Description : This command will email (or display in terminal) the top 25 mailboxes, ordered by size. Strangely – Plesk doesn’t seem to have any kind of Mailbox Size report, and will only show you the domain mailboxes combined.

Simply SSH into your Plesk server and run the following :

cd /var/qmail/mailnames
du -hs --block-size=1024K */* | sort -nr | head -25 | mail -s 'Top 25 Mailboxes by Size' [email protected]

And if you wish to display on screen :

cd /var/qmail/mailnames
du -hs --block-size=1024K */* | sort -nr | head -25

The first script could be set up as a handy Cron job to send you a weekly / monthly report.