WordPress MU

I have set up Wordpress MU in the root directory of http://www.mainaccount.com

At the same time, I have say 3 add-on accounts, http://www.addon1.com, http://www.addon2.com and http://www.addon3.com

If I created a subblogs for each of these 3 add-on accounts, http://www.addon1.mainaccount.com, http://www.addon2.mainaccount.com and http://www.addon3.mainaccount.com via the site admin, the blogs don't load.

How can I map or redirect http://www.addon1.mainaccount.com to http://www.addon1.com

If you add the blogs as subdomains, you need to set up the wildcard subdomains mentioned in both the readme and the install setup screen.

If you eventually want those blogs to have their own domain, you also need the domain mapping plugin.
http://wordpress.org/extend/plugins/wordpress-mu-domain-mapping/

But the subdomain blogs have to work first.

when you say " http://www.mainaccount.com " do you mean the public_html root and the domain name used for your hosting account?

I have set up WPMU sub-domain builds in such circumstances but hosts are not happy about it (still never figured out why) but for webspace management and simpler visual admin, I've always found it much easier to do something like this -

/public_html/index.php-for-the-next-line-singleuser-wp
/public_html/any-old-folder-name/a-singleuser-wp-install-in-here
/public_html/first-active-wpmu-domain-folder/the-wpmu-files
/public_html/second-active-wpmu-domain-folder/the-wpmu-files
etc

In the above setup, you "shield" your hosting account domain name behind a single user WP install one folder level down, and only have the index.php in public_html root, mapped from the wp-admin as the home page (codex has an excellent step-by-step), this helps spot any nasty file additions in your hosting root a lot easier than dumping a WP install in there.

Then the rest of your add-on domains each go in their own folders under the root, mapped from the cPanel add-on domains tool, which is where you set the wild cards for sub domain installs (or not).

The main reason this is a "best" practice is because when adding those add-on domains, they are each made into a sub-domain of the hosting account domain, PLUS when you add them, you have to give them each a username, and that username is also made into a subdomain of the main hosting account domain.

Roll all that lot together and you get a nasty mess of add-on domain and user subdomain names, mashing up with the blog subdomain names by putting WPMU in as a public_html root-level subdomain install (essentially making everything a sub-domain of the root WPMU) - it'd be an admin & security nightmare - you could end up with publicly accessible addresses like cgi-bin.domain.com or tmp.domain.com potentially even wp-content.domain.com (yes I know the index.php should block it, but deletions do happen) and so on.

My recommendation would be don't do it - keep your hosting account domain name private from the world(or use it for email only), or use a single user WP install for something that's NOT going to attract a lot of traffic (or hacker attention).

Gaz