We are asked frequently "what database should I use?" Now since the question is being asked, usually that means you don't have one and the field is wide open. Though you can convert to other database types later, it is better if you can look at your future needs and plan based on that. This might take a bit more cost and setup, but if you are planning on growing your lists and abilities, it is the best course. The following is a list of databases with their advantages and disadvantages
Microsoft Access - This is a "file" based database which is a great start and may actually be all you need. If you are primarily sending out emails, don't have a ton of responses events, than this database is great. We have actually seen it work for many years for large situations. An MS Access file is very stable, easy to backup (one file), and portable. The disadvantages is that with heavy use the file can become corrupted but very rarely. You do need to compress this file so that the database does not get too inflated, especially if you are adding and deleting a lot of records. Some people have used an Access database for the database back-end for Websites, and that may be OK, but if it is used with an active webserver and Campaign Enterprise at the same time there can be a chance of deadlocks (trying to access the same info at the same time). Since many processes may be accessing the database file at one time without "each other's knowledge", there is the potential for collisions. BUT, don't worry about this until it happens. Access is a great solution and will be support by Microsoft for many years to come. MS Access is not free but it is usually $100 or part of the MS Office Professional package.
Microsoft SQL Server - This system is a true client-server database. Since the server takes requests from many different processes and lines them up in a queue, these requests are handled in an orderly fashion and avoids a lot of the problems that a single-database file has. Advantages are that the SQL server can be installed on the same or a different computer than the one running Campaign Enterprise so you can distribute the workload. It also allows you to have your webserver, database, and email sending system separated. We always recommend you use an SQL server like this whenever possible. This system can cost from $995 and up for MS SQL Server 2012.
Microsoft SQL Server Express - This free database functions just like the full SQL server above, but they have a database volume size limitation and it will only use on CPU core. The limitations of the Express versions change each release, but many will find this system to be more than sufficient.
MySQL - This free database is created and maintained by the public domain. Many people use MySQL with Campaign Enterprise successfully. Most of the time people use ODBC to connect to the database but there have been OLEDB providers available too. MySQL will use multiple cores on your computer and there is not a limit on the database volume size like MS SQL Express. If you don't like Microsoft products and want a good free SQL database then MySQL is a good choice.
Oracle 11g - Oracle works well with Campaign Enterprise. You will need to be experienced setting up database connections using their ODAC connector. You can use a personal version of Oracle for free. The full versions of Oracle have a lot of different pricing structures so it is hard to quote.
DB2 (AS 400) - This database is for IBM mainframes. Campaign Enterprise has connected to this type of database but it is mostly used large companies with established systems.
Many Others - Campaign Enterprise can connect to any database that has an ODBC or OLEDB connector. We have successfully seen it work with Foxpro, Filemaker, and even text-based files. These databases many times do not allow for outside writebacks so if you are trying just read information from a database than these will work but they are not recommended.