more info:
The Centralized Mail server is configured on the basis of a regular Plesk server. Just like a regular Plesk server, it can be installed either standalone (on a separate host) or on one host with Plesk Expand.
You can use the following Plesk versions (among versions available on the moment of the release notes publication) as Central Mail server:
* Plesk 8.1.x for Linux/Unix
* Plesk 8.1.x for Windows
* Plesk 8.2.x for Linux/Unix
* Plesk 8.2.x for Windows
You see, both Linux/Unix- and Windows-based hosts can be used as Central Mail server. Any Central Mail server (Linux/Unix- and Windows-based) can serve for any Plesk server (Linux/Unix- and Windows-based). But there are some limitations, see them below:
* ATTENTION: You CAN NOT migrate mail content (mailing lists, mail boxes, mail groups, autoresponders, etc) from Plesk for Windows server to Central Mail server. You also can not migrate mail content to Windows-based Central Mail server. Only clean Plesk servers can be connected to Central Mail servers in these cases. Otherwise, Plesk users will loose their mailboxes (with content), mailing lists (with content), etc..
See the Plesk Installation Guide for instructions on how to install the Centralized Mail server (the installation of PSA API RPC is a mandatory step). Then return back to follow the instructions below:
1. 1) Complete the Plesk postinstallation process.
2. 2) Make sure that you have added a SHARED default IP address to the Centralized Mail server IP Pool.
3. 3) Make sure that you have removed all clients (including the one named 'My Domains') from the Centralized Mail server.
4. 4) Install the proper Plesk license key on the Centralized Mail server. It should allow to create as many domains as this server is going to serve.
5. 5) It is highly recommended to switch the Cenrtalized mail server to using full POP3/IMAP mail accounts names. Login to the Centralized mail server, go to "Server > Mail" page and enable the "Only use of full POP3/IMAP mail accounts names is allowed" option. Unless this option is enabled, there might be a situation when one mail user can read mail of another mail user (if they have the same password).
When this feature is activated (a Plesk server is assigned to the Centralized Mail Server), the 'Remote Mail' button appears in the Plesk Control Panel of each domain user residing on the assigned Plesk server. By clicking this button in the Plesk control panel, users can open a special page where they can manage their remote mail settings.
http://download1.swsoft.com/Plesk/Expand/2.2.1-Release1/doc/expand-release-notes.html