I'm assuming your definition of doorway pages is setting up multiple pages
with similar content, optimized for various search engines? If this is the
case, that technique lost favor with the search engines years ago and could
result in penalties.
Mirror pages where the same content is on multiple web sites can also run
into the same problem if it is set up to scam search engines. However, the
same article on different web sites works fine.
Coulson, "The E-Business Tutor"
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Private Reply to Garland Coulson