Another problem can happen when you use cookies. If not done correctly, your user’s cookie won’t be available to the website when they were stored under www.domain.com and he uses domain.com the next time he visits. See the cookie specs for more details.

A quick research led me to a solution for apache that I didn’t like too much. It involves using mod_rewrite. mod_rewrite is a great tool, but there’s a better solution for redirecting to your main domain from subdomains or second level domains. Simply use a catchall virtual host in your apache host configuration file(s) to do the redirects. This will solve all the SEO, caching and cookie issues, and it will save some CPU cycles compared to the mod_rewrite or higher level solutions.

# NameVirtualHost *:80
 
<VirtualHost *:80>
    ServerName www.domain.com
    # This is your main domain
</VirtualHost>
 
<VirtualHost *:80>
    ServerName domain.com
    ServerAlias *.domain.com
    # This is to make sure that foo.domain.com gets redirected too
    # If you want to use more virtual hosts on subdomains,
    # just define them earlier
    Redirect / http://www.domain.com/
</VirtualHost>

Please refer to the mod alias docs to decide which Redirect you need, this example uses a 302.

For lighttpd you can use this:

$HTTP["host"] =~ "domain\.com" {
    $HTTP["host"] != "www.domain.com" {
        url.redirect = (
            "^(.*)$" => "http://www.domain.com$1",
        )
    }
}

By the way, if you’re an IIS user, you might want to read this.

After some digging I found the problem: 301 redirects don’t pass POST parameters. And when I configured the mailing list I set the domain to nkuttler.de. So mailman sets the form action to http://nkuttler.de/foo/bar, this gets redirected to the correct domain, but the POST data is gone. How do you change the web host? I couldn’t find anything in the admin interface, it looks like you have to do it on the command line.

cd /var/lib/mailman/bin
./withlist -l -r fix_url list -u www.nkuttler.de/

This is the precise command for Debian, on other distros you’ll have to find the correct location.

Update: I’m not quite sure how I missed it, but the host_name parameter should allow you to change this setting as well. For other questions about the default URL you can also read the Where can I change a list or the default URL used for the web interface? FAQ entry.