2 domains seo link building

Question

I have 2 domains

www.my-domain.co and www.mydomain.us

Both are pointing for the same server, for example if you run

www.my-domain.co/file.html

its the same with

www.mydomain.us/file.html

Now ... i began the seo for www.my-domain.co, submited in webmaster tools, sitemap, links ... etc. Supposed www.my-domain.co will rank good for "my domain". After 1 year i change the domain from webmaster tools to www.mydomain.us, wich has no links pointed to him, and now the question come:

If i begin the link building(dofollow blogs,formus,link directories ... etc) once more on www.mydomain.us it will get double link juice??

Answer 1

What you'll get is duplicate content issues. That's not good. You need to choose which domain is your primary and do a 301 redirect from the secondary domain to the primary domain. Then you should solely seek links to your primary domain. But if someone points a link to your secondary domain it will count towards your primary domain with only a small dampening factor. This also applies to existing links so if you do switch domains the old links will still help you (minus the dampening factor).