Multi Domains Question

[Michael.A]

here it goes .....

rewriteengine on
rewritecond %{HTTP_HOST} ^(www\.)?other1-domains.com$ [NC] 
rewritecond %{REQUEST_URI} !^/forum/
rewriterule ^(.*)$ "http://main-domain.com/forum/" [R=301,L]

rewritecond %{HTTP_HOST} ^(www\.)?other2-domains.com$ [NC]
rewritecond %{REQUEST_URI} !^/forum/
rewriterule ^(.*)$ "http://main-domain.com/forum/" [R=301,L]

rewritecond %{HTTP_HOST} ^(www\.)?other3-domains.com$ [NC]
rewritecond %{REQUEST_URI} !^/forum/
rewriterule ^(.*)$ "http://main-domain.com/forum/" [R=301,L]