Domain aliases causing duplicate content / false link penalty?

[circusboy]

We have 3 domain aliases pointing to our main site.

So, domain1.com, domain2.com and domain3.com all point to maindomain.com. Domain1.com and domain2.com were aliased about 8 months ago, domain3.com about 3 months ago.

These were set up as domain aliases through our hosting company.

While checking/searching for anyone stealing our content, I noticed that Google was listing domain1.com AND maindomain.com as having the same content? (duplicate pages - same page names, everything... except the main domain name, obviously)

Even worse, in WMT I noticed when checking my EXTERNAL links, it showed domain1.com, domain2.com, and domain3.com ALL as being external sites linking to maindomain.com.

This may explain our major ranking drop in the past few days?

#*$! did I do wrong - how do I fix it? Please help.

[tedster]

Sounds like the "pointing" or "aliasing" is not being done with a 301 Permanent Redirect. Any other method except for the 301 Permanent Redirect runs the risk of creating indexing and ranking troubles by creating duplicate urls for the same content.

it showed domain1.com, domain2.com, and domain3.com ALL as being external sites linking to maindomain.com.

They are external to your main domain - they have a different domain name.

[circusboy]

Thanks Tedster; I'll check out how the host company is doing the redirects.

[g1smd]

Don't forget to cater for both www and non-www for all of those domains.

[circusboy]

Thanks Tedster and g1smd;

Sure enough, the domain aliases were not done with 301 redirects. I implemented proper domain management, set up the 301's, and sent in a reinclusion request explaining the situation.

Time will tell - I'll update if anything happens.