FreeBSD email users - migrating to Plesk

[Brent999]

Hello, this might be a laughable question but I seem to be faced with an ugly problem. I have to move about 600 email users from a FreeBSD machine where they exist having been created solely with the adduser command, to a new FreeBSD machine running Plesk 8.1.0. Is there an elegant way to do this (using master.passwd for example), given that I do not have record of the passwords?

Or, am I faced with a few hundred phone calls to make or take?

Thank you kindly,

Brent