I don't have version 5.x but have a license from 2005 for sale.
It can be used for getting the latest version of Atmail with a 50% discount, see: atmail.com/upgradeatmail.php
This would save approx $1000 for most purchases.
I paid $2005 for the following:
Email-Server & WebMail for Linux.
User License = 1000. Domain License = 4.
Modules = Sub-Admin/Multi-WebAdmin, POP3, SMS & WAP.
978 SMS credits remain available (value approx $50).
The license is being verified by webhostingtalk (many thanks Alex).
I can accept payments via paypal, escrow.com & Google Checkout (debit/credit cards).