VPOP3 uses PostgreSQL as its back-end database. This database stores everything from settings to message content. The only things currently not stored in the database are quarantined messages and archived messages (future versions of VPOP3 may store quarantined messages in the database as well).
VPOP3 v5 and later require PostgreSQL 9.1 or later. VPOP3 v7 and later require PostgreSQL 9.5 or later.
The VPOP3 installer will install a copy of PostgreSQL in the 'pgsql' subdirectory of the VPOP3 installation folder. It is installed as a Windows service called VPOP3DB which runs as a Windows user called vpop3postgres. For security, this Windows user has full permissions to the 'VPOP3\pgsql\data' directory, read only access to the other 'VPOP3\pgsql' directories, and no access elsewhere on the disk
The installation of PostgreSQL into the VPOP3 directory is purely for ease of use and installation: it is not important for VPOP3 that it is installed this way. In fact, the PostgreSQL server could be installed in another directory or drive on the same PC, or even on a different PC. You could install PostgreSQL on a Linux computer or NAS server or whatever, as long as it is of an appropriate version and has suitable performance (including network connectivity).
This section of the manual is for advanced users who may want install PostgreSQL elsewhere. It will not go into step-by-step details - if you need those, then you should probably not be doing this, but it is there for advanced users who may know about PostgresSQL and want to install it in a different location or different PC and just need to know what VPOP3's requirements are.
As mentioned, VPOP3 requires PostgreSQL 9.1 or later for VPOP3 version 5 or 6.x and PostgreSQL 9.5 or later for VPOP3 version 7 or later. Note the 'or later's, so you could use PostgreSQL 9.3 with VPOP3 version 5, and it will work fine. VPOP3 requires features added in the mentioned versions of PostgreSQL, but those features are present in later versions of PostgreSQL as well.
The VPOP3 installer installs a 32 bit version of PostgreSQL, but you can use a 64 bit version without any problems at all.
The requirements for an installation of PostgreSQL to be used with VPOP3 are:
•It must be an appropriate version of PostgreSQL
•There must be a PostgreSQL user/role created which needs a password to log in. This must be the owner of the database VPOP3 uses.
•The database must be created with the 'SQL_ASCII' encoding (eg 'CREATE DATABASE vpop3 ENCODING 'SQL_ASCII' TEMPLATE template0;')
•The database must be accessible from the VPOP3 computer (ie set the 'pg_hba.conf' file correctly)
If you do this before installing VPOP3, then tell the VPOP3 installer that you don't want to install the Database component. It will then ask you for database connection information.
If you do this after installing VPOP3, then you should migrate the database over to the new database by using a pg_dump/pg_restore process. You can then edit the VPOP3.INI file to set the database connection settings.