VPOP3 is available in three editions, VPOP3 Enterprise, VPOP3 Basic and VPOP3 Home User.
VPOP3 Enterprise is the most feature-rich version of VPOP3. As well as POP3 & SMTP support, this edition includes IMAP4 support to allow mailbox sharing and accessing your full mailbox from multiple devices at once. If users want to be able to share a mailbox or access their email from their mobile phone then we strongly recommend that you use VPOP3 Enterprise.
VPOP3 Enterprise also supports multiple calendars using the CalDAV standard and other 'enterprise' features such as using an external database for distribution list membership and address books. VPOP3 Enterprise also supports SSL/TLS connections to its own services as well as SSL/TLS connections to remote servers.
VPOP3 Basic is a reduced-functionality version of VPOP3. It does not support IMAP4 for email, just POP3, which does not allow shared access to mailboxes or access to your full mailbox from multiple devices. VPOP3 Basic supports the CalDAV standard, but each user can only have a single calendar.
VPOP3 Basic supports SSL/TLS connections to remote servers, but does not support installing a certificate for SSL/TLS connections to its own services.
VPOP3 Home User is a cut-down version of VPOP3 Basic. It only supports 5 users (and cannot be upgraded above that). Some other functionality such as LAN Forwarding is also disabled. We don't recommend that the Home User version is used by businesses.