# forward from domain aliases
RewriteEngine On
RewriteCond %{HTTP_HOST} ^(www\.)?domain1\.com [NC,OR]
RewriteCond %{HTTP_HOST} ^(www\.)?domain2\.com [NC,OR]
RewriteCond %{HTTP_HOST} ^(www\.)?domain3\.com [NC,OR]
RewriteCond %{HTTP_HOST} ^(www\.)?and_so_on\.com [NC]
RewriteRule (.*) http://maindomain.com/$1 [R=301,L]
# END forward from domain aliases

http://www.torkiljohnsen.com/2008/01/16/some-easy-use-of-mod_rewrite/

Forward users from your alias domains to your main domain automatically. Nice to have if your site has got one or more aliases. Notice that all the domain aliases have [NC,OR] at the end of the line, while the last alias and_so_on.com just has [NC].

Insert the code in your .htaccess-file in your website's root folder.

Forward from domain aliases to main domain

url, htaccess, apache

Apache