Twitter continues to becoming more and more popular these days, especially for businesses. As a business, you want to keep your followers interested, and in-tune with all your media outlets. One great way is to use Twitter's direct messages. If you follow CATS on twitter, you'll get a direct message from us right away letting you know how you can keep in touch and get all of our updates.This kind of response is helpful to build a relationship with your followers. We searched google, and there were slim pickings as far as auto-responding software, so we decided to develop this inhouse. I'll be showing you how to build this into your email. To implement this setup, you'll need the following things: An email account on a Linux/UNIX system A twitter account registered for that user php-cli (or another scripting language if you want to re-implement it) curl When I was asked to develop the auto-responder, my first thought was "I'm getting this email from twitter that says 'George is now following you on twitter'. I bet I could use regular expressions to solve my case, but who knows when they'll change the format of the email or something...". After some investigation, I looked at the headers of the email, and I was delightfully surprised to see: ... X-Twitterrecipientscreenname: catsone X-Twittersenderscreenname: George_C X-Twitteremailtype: is_following X-Twitterrecipientid: 16535056 X-Twittersenderid: 16600001 Errors-To: Twitter <twitter-follow-twitter=catsone.com@postmaster.twitter.com> X-Twittercreatedat: Tue Mar 09 17:04:37 +0000 2010 Bounces-To: Twitter <twitter-follow-twitter=catsone.com@postmaster.twitter.com> X-Twitterrecipientname: CATS App Track Sys X-Twittersendername: George C ... This is something I can work with. I don't need to do any heavy lifting for this. The main reason you need a unix email account is so that you can create a .forward file. This file tells your mail server to redirect your email messages to another email address, or in our case, a PHP script. The contents of the file is very simple. Assuming the user's name is twitter and our processing script is located at '/home/twitter/twitterReply.php', All we need in that file is: "| /usr/bin/php /home/twitter/twitterReply.php" You can read more about the ".forward" file at http://www-acs.ucsd.edu/students/email/dotforward.shtml The actual PHP script will essentially read the email headers to determine if the email is a "Following" email and the user ID of your new follower. If we can determine both, then we're going to use the Twitter API to send a message to that user. I'll leave all the code explanation to the comments since the whole script is just about 50 lines. Note: Feel free to include HTML tags in the message such as <a href="www.example.com">My Site</a> because it's running through urlencode(). <?php</p><p>// Config Options$username = 'andy';$password = 'secret';$message  = 'This is the message your followers will get.';</p><p>// Read the email message from standard input$fp = fopen('php://stdin', 'r');</p><p>// These default to false$isFollowing = false;$userID = false;</p><p>// Read lines until we get past the headerwhile($line = fgets($fp)){    // We just need to match a static header signifying that they are now following us    if (trim($line) == 'X-Twitteremailtype: is_following')    {        $isFollowing = true;    }</p><p>    // If we haven't found the userID yet, then use a regular expression to pull out the userID    // Sure we could have used strpos() and substr(), but I <3 regular expressions.    if (empty($userID) && preg_match('/X-Twittersenderid: (d+)/', $line, $m))    {        $userID = $m[1];    }</p><p>    // Once we're finished reading the headers, then we're done.    if ($line == "n")    {        break;    }}</p><p>// Close the file handle properlyfclose($fp);</p><p>// Make sure this email is an "Is Following" email and we found a valid userIDif ($isFollowing && $userID){    // urlencode the message because it's going to be a POST variable. The userID is just a number, so it's fine.    $message = urlencode($message);    // Use the "which" command to find the proper path for curl.    $curl = trim(`which curl`);    // Finally, call curl using our username and password, the userID, and the message to the Twitter API.    // I added a redirection to /tmp/twitter.debug.txt so we can check what the last api call returned.    exec("$curl -u $username:$password -d 'user=$userID&text=$message'         http://twitter.com/direct_messages/new.xml > /tmp/twitter.debug.txt");}?>