Dada Mail validates an email address in a variety of ways. The simplest way is to look at the actual address itself and see if it's form is correct. When an address is subscribed to a list, Dada Mail also sees if the address is already subscribed and if the address is blacklisted. A blacklist is a separate sub list containing addresses that aren't allowed to subscribe to the list. Dada Mail can also do a mx lookup on the domain of the email address itself. An email address whose form is valid does not necessarily mean that the address is real:
example: justin@hlkjhlkjhlkjhlkjhlkjhlkhlkjhlkhlkhlkj.com
This battery of tests are issued to ensure that your subscription lists stay clean. Even if an address is no longer valid because an email account is closed, Dada Mail does include a bounce handler, called Mystery Girl, that can be installed separately. If you don't have the bounce handler installed, you can still unsubscribe email addresses en mass.
Dada Mail sends mail in two ways. The first way is by "piping" a message to your servers command line sendmail utility. Piping just means passing information between two programs; in this case for Dada Mail to the sendmail utility. The other way is by sending messages to your SMTP server, just like you do with a program like Outlook or Eudora. This has the advantage of using a separate server to send messages out.
Mailing list messages sent from the web-based control panel are "forked" off from the main program. This just means a separate copy of the program is started up just to handle the sending of the messages. This allows you as the list owner and your subscribers to interact with Dada Mail without the danger of stopping a list mailing, which could take many hours.
List subscribers are generally saved in a plain text file, with one email address per line. Dada Mail has been heavily optimized to work with this simple file format efficiently and safely. The advantage of this is that you can interact with the subscription lists yourself by hand or couple entirely different programs to it.
Dada Mail can also be set up to use an SQL back end to save its list information.This has the benefit of being enterprise-level bulletproof. In the near future, you will also easily be able to store information other than just the subscriber's email address.
Dada Mail is written in Perl. Perl is available on almost every operating system in existence. You use Dada Mail via a web browser. This means that as long as you have a connection to the internet and a browser, you can use your copy of Dada Mail.
Much of what makes Dada Mail so powerful is that it takes advantage of GPL-based software. This is something other commercial mailing list managers can't use, since doing so would break the GPL license.
All of the source code for Dada Mail is available for free to download and change. If you have a similar project in mind, Dada Mail is a great way to start that project. Why reinvent the wheel? We did that already for you!