Just found this neat tool on the internet, called putmail.
It is a SMTP Client. Now, you may wonder what exactly an SMTP client is, and why you need one. Well, if you are Unix/Linux user and use tools, which follow the Unix philosophy, then you end up with tools that do one task only.
This idea reaches back to times when resources used to be rare and expensive and programmers therefore tried to spare those resources. One way to do this was to write highly modulized tools that could be combined with each other, each of them processing one task and then handing the result over to the next tool. This made it possible to get a chain of tools that combined with each other made up a whole process line.
If you use such tools for your daily mailing issues (e.g. mutt), then you will definitely need a MTA, which in the end leads up to a SMTP capable tool. Most of the people use such tools as sendmail, exim, postfix, etc. But those are Mail-Server tools, so eventually with those tools you could run full mail servers that provide mailboxes for different users, authentication functionalities, sending mails, receiving mails, and forwarding of mails. Now this is something, a mail admin would want to use for his own domain, but it may be a bit oversized for someone who just wants to do some mailing and has an account at one of the plenty free mailers, or elsewhere (besides it is even a security risk, as a SMTP server is a service that runs all the time in the background and opens ports to the internet, which make them to potential security wholes if not configured or programmed well).
But there are also other reasons why you may want to use a mail client. Let’s say you have some tasks you want to perform regularly on any computer and be informed by the results via email. Nothing’s easier than that. And as putmail is written in python it is available for any system where Python is available (this includes Windows, Mac, and a lot of more exotic systems). So you could write a small script, let’s say a batch file, or a visual basic script, using putmail to send the IP of a computer to your mail account whenever the computer restarts, giving you the ability to access your machine through the Internet wherever you are.
These are only some usages you could think of. Anyway, as always the boundaries of usage are only set by your thinking.