Well, I haven't yet changed MTAs, it really isn't that important, though I hope to do it within a few days. I am looking at ProgreSQL as a database backend.
I may have a project to do, building a better app for certain stores to use. Currently, the FoxPro app in use in many stores calls for $7,000 a license. I figured I could do the same in an open database and a webserver.
That is, leave the structure and data of the backend open for all to see (hey, it's their data!) but close up the code that accesses it (PHP, or the like). Then just give these people a complete package, that includes a computer (maybe even Dell with (hardware) support), an OS (Debian Gnu/Linux), webserver (Apache), and Database (ProgressSQL, MySQL).
The advantage of a Linux box is obvious. No cost for an OS, it's more likely not to crash, and can be administered remotely.
The advantage of having a webserver is that anyone can connect from their computer, as long as it can connect to the network, and has a web browser.
The database is required to hold the data, but keeping it open in in tune with my belief, that the application may be mine, but the data is theirs. It also allows the use of other access tools, and not just one proprietary interface (or a really slow ODBC connection).
So, when looking for a database, I am used to Oracle. Well, that costs a bit too much. So, MySQL and PostgreSQL are the obvious choices. I guess I like PostgreSQL more because it is free no matter where it is used.
Now I must come to terms with making money off free software.