I want /sites/mysite directory to handle mysite.local, mysite.com and mysite.org

I often say with regards to multisite Drupal installations, "If your solution to a problem is to make a symbolic link, you're probably doing something wrong." But this is an exception.

First off, I suggest you name the site directory after the "normal" domain name for the site, whatever that may be. Let's say that's example.com. But you want to use the same site directory for example.org or example.local. So simply create symbolic links with those two names which link to the example.com directory. Piece of cake.

If you're not familiar with symbolic links, think of them as aliases in Mac OS parlance, or shortcuts for Windows - file system entities which simply point to some other file system entity. To create a symbolic link to example.com with the name example.org, type this at the command line:

ln -s /path/to/example.com /path/to/example.org

If you're using Windows, I think you can simply create a shortcut inside Windows Explorer to achieve the same effect. However, if you're on Mac OS X, creating an alias via the Finder will not work - you will have to open up the Terminal and do it that way.

Note that this can cause issues with attached files, and you need to be mindful of paths in content too (Pathologic may help in that regard). Namely, attached files are stored in the {files} table of the database using the path of the site in use as the file was uploaded. For example, if you upload a file while accessing the site at http://example.local, the file probably won't display correctly when you look at the site from http://example.com. A fairly simple SQL UPDATE/REPLACE command can fix this, but it can be a pain to do often.

so your sites folder looks like

all
default
mysite1.dev
mysite2.dev

Does either mysite1.dev or mysite2.dev work? If you remove mysite1.dev and mysite2.dev folders do they pickup the default settings?

In case anyone else finds this thread searching or otherwise, the original post was about serving up multiple sites from a single multisite directory and the troubles when the multiple sites don't match Drupal's expected discovery path.

The best solution was solved in core for D7 by using the sites.php file which was introduced in http://drupal.org/node/231298.

This lets you use sites/sites.php to directly specify which directories you want to use.

which would allow http://mysite.local to use the settings and files in sites/mysite.com without affecting any sites already using that directory, plus unlike the symlinks, all information will be stored in the database as sites/mysite.com so that file paths and module paths will be where you want them to be.

There is also a valid patch for D6 in that issue and it is well excepted that it works, but D6 isn't accepting new "features" so it won't be included.