Automatically updating SMTP servers with location on Mac OS X

or

The dirtiest script I have ever written

Matt Webb matt@interconnected.org

Ingredients: kicker-smtp.xml and changeSMTPServers.pl.txt. Find out what they do further down.

The problem

We want to change the current SMTP server to a more appropriate one every time the network location is changed on Mac OS X.

Background

Network System Configuration on Mac OS X has a high level Carbon framework called System Configuration which you can learn about at Apple's System Configuration Overview technote. It has a low level interface for shell-scripts governed by configd.

All of this information is pinched from this page on culater.net, but in a nutshell:

• configd is a daemon that keeps track of all network configuration information.
• The network configuration information itself is kept in /var/db/SystemConfiguration/preferences.xml, but it's a bad thing to talk to that directly.
• There's a command-line tool called scutil that lets you look at configd information in a key/value + dicts sort of form.
• configd lets you set up notification agents, which are triggered every time a specified key (the same key that scutil sees) is changed. This is done by editing the notification file, which is /System/Library/SystemConfiguration/Kicker.bundle/Resources/Kicker.xml

Solution

Notification

Add this xml fragment to the bottom of /System/Library/SystemConfiguration/Kicker.bundle/Resources/Kicker.xml. Put it just inside the last </array>. Do this as root.

In that xml fragmant:

• Setup:/ is the key we're interested in. It contains a dict containing the name of the current location, so it changes when you change location.
• The script specified just after execCommand will be called when Setup:/ changes value. Change this path to where you're going to keep the script.
• The integer just after execUID is my user's uid. Change it to yours.

Now reboot. I'd love to know how to restart configd and all its associated processes from the command line, but I can't figure out how.

Changing the SMTP server for mail

This is done with Applescript. Using the defaults system might work, but I'm not sure how to make Mail.app read the new values. So Applescript it is.

The script that's mentioned in the xml fragment above is here: changeSMTPServers.pl.txt. Put it wherever you said in Kickers.xml, and chmod it to execute (and knock the .txt off the end, obviously).

Configure the script

At the top of the script, there a hash called $smtp_for_location which maps existing network location names to existing SMTP servers. Change it to whatever you'd like.

This bit is important: The SMTP servers must be known by Mail.app already. Go into Mail, choose Preferences, edit an account and look at the Outgoing Mail Server list. Choose Add Server. The SMTP server mentioned in the script is just the identifier for all this information -- and it's the hostname used as the identifier.

The next bit of configuration is the $accounts_to_change list. Any Mail.app account name listed in here will be changed whenever the location changes.

What the script does

Gets the current location. Because configd doesn't pass through what's changed, only that something has changed, the script calls out to scutil and looks up the UserDefinedName of the current location. This is the location name you set in the Network control panel.

Puts together an Applescript. The Applescript needs to know the new SMTP server and which accounts to change. Those are put in as properties. The Applescript then cycles through the SMTP servers that Mail.app knows about, making sure this new one exists. If it does, it grabs the server object. It then cycles through the accounts, and changes the relevant ones if necessary. It also spits back some useful information about what was changed, but who knows how to pick that up.

Runs the Applscript. The Applescript is run via a backticked osascript. Lovely.

Bugs and problems

Mail.app needs to be running.

If you're multi-user on your machine, this script ain't going to work. It runs as a single user, and has no configuration to change to different SMTP servers for different users. Nasty.

Exceptions. Know how to get information back from osascript through configd and back to the user? No? Nor do I. That's a bug.

Guarantees

There are no guarantees. Don't muck around with your system if you don't know what you're doing, I take no responsibility.

Who to blame

Flames and letters of disgust to Matt Webb at matt@interconnected.org.

26 August 2002