Go to Settings → Database → Query

Alternatively, at a command prompt in the VPOP3 directory run

psql

(The password is 'vpop3pass')

Then, type

select username,dataname,datavalue from users.usersettings inner join 
users.users using(usernumber) where datavalue ilike '%searchname%';

(replace 'searchname' with the name you want to search for)

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