To find the 10 biggest messages in your VPOP3 message store:

Go to Settings → Database → Query

Alternatively, at a command prompt in the VPOP3 directory run

psql

(The password is 'vpop3pass')

Then, type

SELECT username, folder, subject, fromaddr, PG_SIZE_PRETTY(size) FROM messages.messages INNER JOIN messages.folders f USING(folderid) INNER JOIN users.users u ON u.usernumber=f.userid ORDER BY size DESC LIMIT 10;

N.B. VPOP3 does not need to be stopped while you do this