Free and all you will need

hMailServer provides all of the important functionality you need to run your own e-mail server. As a user of hMailServer, you get continuous updates and great support from other users and developers in the forum. hMailServer is a free product. Free when it comes to the price, and free when it comes to how you can use or distribute it. hMailServer supports the open email standards POP3, SMTP and IMAP4. This makes the server compatible with most email clients available. hMailServer 4 and earlier versions are licensed as open source under the GPL license. Later versions of hMailServer (version 5 and later) are still free of charge but closed source.

Installation & Configuration

Tired of manually editing .conf and .ini files? Installing and configuring hMailServer is easy and takes only a few minutes. The server comes with an easy-to-use MMC-like administration called hMailAdmin. hMailAdmin lets you add domains & accounts, specify settings, enable virus scanning and so on. The documentation describes the features in detail. If you have any questions, there’s a great user forum full of helping users to turn to. The hMailServer developers answers question in this forum as well. When you seek support at the forum, the average reply time is less than two hours!

Database support

hMailServer supports Microsoft SQL Server, PostgreSQL and MySQL. The hMailServer installation includes a minimal, built-in database server called Microsoft SQL Server Compact. During the installation you can choose whether you want to use the built-in database or a already existing database server. The built-in server saves you the hassle of having to set up and configure a separate database server for hMailServer, but using an external database server may give better performance.

Webmail

hMailServer is compatible with any email client which supports SMTP, POP3 and IMAP. This is true also when it comes to web mail clients. hMailServer can use any web mail system which supports these protocols (normally SMTP and IMAP is used, not POP3). Depending on what server you are running, different web mail systems may suit your needs. For example, some webmail systems relies on the PHP scripting engine (which typically runs under Apache) while other relies on ASP (which normally runs under Microsoft Internet Information servers).

Security

hMailServer is pre-configured to have high security when it comes to relaying and authentication so that no one can use your server to send spam messages. It also supports the very popular open source virus scanner ClamAV. Configuring hMailServer to use ClamAV only takes a single click! The server also supports black list servers and other spam-stopping mechanisms such as SPF and MX lookups.

Integration

hMailServer comes with a COM library that can be used for integration with other software. Using the COM library, it’s possible to write scripts and full applications that utilize the features in hMailServer. For example, you can integrate hMailServer into your current IT-systems so that new employees automatically get email accounts. Both hMailServer Administrator and the PHP web-based frontend uses the COM API to manage the server.

Main features

• POP3, SMTP, IMAP
• Virtual domains
• Built-in backup
• SSL encryption
• Anti-spam
• Anti-virus
• Scripting
• Server-side rules
• Multilingual
• Routing
• MX backup
• Multihoming
• SQL backend
• Web administration

Integrations

• ClamWin
• SpamAssassin

1. Activities

2. Services

3. Broadcast Receivers

4. Content Providers.

The means of communication between the above mentioned components is through

1. Intents

2. Intent Filters

The User Interface elements are by using what are called:

1. Views

2. Notifications

Now, having broadly classified the basics, I would like to give a simple definition for each of them, before we can appreciate the need for each of them.

Activity is the basic building block of every visible android application. It provides the means to render a UI. Every screen in an application is an activity by itself. Though they work together to present an application sequence, each activity is an independent entity.

Service is another building block of android applications which does not provide a UI. It is a program that can run in the background for an indefinite period.

Broadcast Receiver is yet another type of component that can receive and respond to any broadcast announcements.

Content Providers are a separate league of components that expose a specific set of data to applications.

While the understanding and knowledge of these four components is good enough to start development, the knowledge of the means of communication between the components is also essential. The platform designers have introduced a new conpect of communication through intents and intent filters.

Intents are messages that are passed between components. So, is it equivalent to parameters passed to API calls? Yes, it is close to that. However, the fundamental differences between API calls and intents’ way of invoking components is

1. API calls are synchronous while intent-based invocation is asynchronous (mostly)

2. API calls are bound at compile time while intent-based calls are run-time bound (mostly)

It is these two differences that take Android platform to a different league.

NOTE: Intents can be made to work exactly like API calls by using what are called explicit intents, which will be explained later. But more often than not, implicit intents are the way to go and that is what is explained here.

One component that wants to invoke another has to only express its’ “intent” to do a job. And any other component that exists and has claimed that it can do such a job through “intent-filters”, is invoked by the android platform to accomplish the job. This means, both the components are not aware of each other’s existence and can still work together to give the desired result for the end-user.

This dotted line connection between components is achieved through the combination of intents, intent-filters and the android platform.

This leads to huge possibilities like:

1. Mix and match or rather plug and play of components at runtime

2. Replacing the inbuilt android applications with custom developed applications

3. Component level reuse within and across applications

4. Service orientation to the most granular level, if I may say

Now that the concept of intent has been introduced, let me get down to a more formal definition of Intent.

Intent is a bundle of information, a passive data structure that holds an abstract description of the operation to be performed. (or in the case of broadcasts, a description of an event that has happened and is being announced).

There are 2 types of intents which I intend to detail in the next part of this series. Before winding up part 1, I would finally also give you a formal definition of Intent filters.