Simple email server tricks

Let's automate email.

We are continually surprised at how many moderately experienced computer users and developers don't know the basic facts about email. Throughout the coming year, we'll explain a few of the essentials and show working scripts that solve common problems.

Automating the original "killer app"

We start with the essentials. Email items travel across the Internet as plain-text byte streams, formatted according to RFC 822 (see Resources, below). This specifies a simple structure of a header followed by content, with a blank line separating the two. A minimal message might then look something like

     From someone@somewhere.net Tue Mar  6 16:16:00 2001
     
     This is a message.

Items typically have considerably more elaborate headers, including elements such as To:, From:, Subject:, and so on.

This is enough background to understand one of the questions we come across most often: "How can I automatically send out an email item with a Subject (or Cc, or Bcc, or ...) that says X?" In a typical Unix environment, all it takes is a command line invocation

       sendmail -t << END
       From: myaccount@myhost.com
       Subject: This is the subject.
       To: intended_recipient@somewhere.com
       Cc: other_person@somewhere.com
       Bcc: my_records@myhost.com

       Hello.  This is the message.  Goodbye.
       END
   

You can also emit email messages directly from most languages, without an apparent need to invoke an external process such as the sendmail used here. We use this most often when testing email service, and especially in architecting unusual sites; by coding at a lower level, it's easy to access alternative network ports, request unusual relay topologies, and so on. Through the Resources below, you can locate ways to code email transmissions in such other common scripting languages as KornShell, Perl, Python, Rexx, Ruby, and Tcl.

However, email agents including sendmail add a great deal of value that's not immediately apparent. They will, for example, retry transmissions so that temporary breaks in connectivity don't thwart your attempts to get through. Therefore, our usual advice to developers automating most email operations is just to "shell out" and invoke a specialized, external email agent. All the most popular scripting languages make that easy.

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