301 redirects and duplicate content

Is this a problem when having lets say mainsite.com and using 301 redirects from other domains to send over the link juice to mainsite.com? Do those domain 301 redirect become duplicate content?

Thanks for any answer.

The gain you will get from an action like this will be almost of zero value.

Also, there are a few things to check first.

The domains must be relevant, coming from the same niche.

You also have to check each domain backlink profile. The link profile of each domain must be healthy & relevant to your main domain niche.

As soon as the domains will be redirected from your registrar or by you (no content & pages - just a 301 redirect), there will be no duplicate content issues.

Generally, don't expect rankings increase with 301 domain redirects.

Thanks for answer Isaiah.

If the donor domain was under the sanctions of google then most likely you will inherit them. It is much more effective to restore the contents of the site from the web archive and put a link to your primary domain.