Dependency on the php_dba module used to be a real problem for many web admins who tried to install PrivMX WebMail. This essential (low-level) module provides quite fast functions for simple file-based databases, but …this module is often missing on webhosting services. We had to do something with this surprising situation and the best solution in our opinion was to create our own, pure PHP implementation of fast key-value database. Starting from the version 1.1.0, PrivMX WebMail has included such code. It is a little bit slower and this is why the warnings during installation appear.
Source code of our pure PHP key-value database is avaliable here: https://github.com/simplito/ldba-php