Modifying default role on mailboxes

[Tony Kenny]

I am trying to find, or write a script that will modify the default role on Exchange 5.5 mailboxes. I have inherited a system in which for some unknown reason, all of the user roles on every mailbox have been set as a custom role. I would like to change this back to the default "user" role on every mailbox.

I would perform this task manually, however there are several thousand mailboxes, so it only makes sense to script this operation.

Any ideas ?