Most Internet Service Providers (ISPs) already give customers the ability to send and receive e-mail on their servers, so why would we want to own and manage it by ourselves? As you are after all reading this book, you may already have your reasons, but let us examine this question and some possible answers to it.
The most important reason for hosting and managing your own e-mail server is control. For many organizations, e-mail is an important part of the Information Technology infrastructure. Keeping control over your e-mail has many advantages.
If a company has offices in multiple places, you have full freedom when choosing how to connect them. A virtual private network between the offices, Transport Layer Security (TLS) connections between the offices, a single server for all offices, one server per office, and so on.
By keeping your own messaging in-house, you can send messages to each other without having them travel across unsecured lines to and from the ISP. This also gives you a more reliable service if your Internet connection fails, and it avoids unnecessary latencies.
You are not dependent on the competence of the provider's staff. If you manage your own server and need to solve a difficult problem or implement a custom solution for something, you can. Or if necessary, you can hire a consultant to help you.
If the provider goes bankrupt, all of your data resides safely in your server room and on your backup media.
You are not subject to the limitations that our provider may set regarding, say, use of disk space or the maximum size of messages.
You can implement any policies for message archiving, antispam, or antivirus that you choose.
More control requires more responsibility and more knowledge, and that is where this book comes in.
These hopefully compelling arguments aside, there are also downsides to hosting your own e-mail server. This is a task that requires a certain level of knowledge and commitment, and so should not be undertaken by everyone. With your own server, you are not only responsible for the service you provide to your users, but you also have a responsibility towards the whole Internet community. An ill-configured e-mail server can help worms and spam to spread, which is not only is a disservice to the community but can also get your server blacklisted. Even though a properly set up server can run for years without requiring much maintenance, you must keep yourself reasonably updated and be prepared to act upon new threats that may arise. This is not meant to scare you off, but just to make you think carefully before embarking on this project.