Suggest a query

Hi friends,

I have a  table in my postgre  data base.  In that table I have a field
called  folder_name  whose value will be full path of the mailbox . For
example    /gomathi/ax/ay/mbox  is the value of folder_name,
where mbox is the mail box.  I want  to find out all the mail boxes
whose parent is mbox.

Actually I can try as

Select folder_name from  mail_box where  folder_name like 'mbox/%' ;


but  I should not hard code the folder_name as given above  after
'like'.   SInce folder_name  comes as a parameter to the program the
value cannot be hardcoded.
Please suggest an alternative way to find out the sub folders of folder
mbox.


Regards,
gomathi