Some users registered with the server OS may access their mail accounts using legacy mailer applications that read mailbox files directly. Since these mailers bypass Internet protocols, the CommuniGate Pro server has no control over those mailers.
The CommuniGate Pro Server keeps all user Accounts and Mailboxes inside its "base directory". On a properly configured system direct user access to the base directory is prohibited to ensure that Account Mailboxes and other Server files stay intact.
When you create a CommuniGate Pro Account for a local user who needs mail access via legacy mailers, select the Legacy INBOX option. In this case, the INBOX Mailbox will not be created inside the CommuniGate Pro base directory. Instead, the INBOX Mailbox location will be taken from the Domain Settings. Usually, you specify /var/spool/mail/* - the "standard" location where legacy mailers expect to see user Mailboxes.
When the Server accesses these Legacy Mailboxes, it uses the OS file-locking mechanism to synchronize its activity with legacy mailers.
Note: legacy mailers were not designed to support simultaneous access to mailboxes. They can destroy data in your mailbox if you open two legacy mailer sessions with the same mailbox and delete messages in one of the sessions. CommuniGate Pro cannot fix this, since these mailers bypass the server, it can only guarantee (using file locks) that legacy mailers do not destroy a mailbox while CommuniGate Pro is working with it.
For more details, see the Mailboxes section.