How To 301 Redirect Multiple Domains Into One Domain
The Problem
If you need to do a 301 redirect between multiple domain names, and force all domains to direct to the "www", use the following code in your .htaccess file.
RewriteCond %{HTTP_Host} ^(www\.)?secondary-domain1\.com$ [NC]
RewriteRule ^(.*)$ http://www.maindomain.com/$1 [L,R=301]
RewriteCond %{HTTP_Host} ^(www\.)?secondary-domain2\.com$ [NC]
RewriteRule ^(.*)$ http://www.maindomain.com/$1 [L,R=301]
RewriteCond %{HTTP_Host} ^maindomain\.com$ [NC]
RewriteRule ^(.*)$ http://www.maindomain.com/$1 [L,R=301]
And that's how you would do a 301 redirect between multiple domain names, and force the "www" version of your main domain. The code above is for a .htaccess file on an apache server.