Here's what you need to know before deciding to redirect other domains to a primary domain for SEO.
Foremost, let's get some things straight. Pointing multiple domains to a single website implies redirecting '301' or other redirects from extra domains of the client's website. The client's website does not resolve all the redirected domains. When a single website answers multiple domains, it creates numerous websites with duplicate content, which is terrible for SEO.
When to Redirect Other Domains to Your Principle Domain
To redirect other domains to the client's main website, you need to know the answer to these questions:
1. What is the origin of the domain?
2. How long has the domain existed?
3. Do the domains have their own websites?
Here's what to do before redirecting other domains to your primary domain:
If any other domains have been standalone websites or run by external parties in the past, you need to pull up the domain history. Pull up a historical backlink of the profile that traces as far back as possible. Get new backlink profiles for every domain, and in the profiles, be wary of questionable elements. Check if the former domain involved procuring external links. The last thing anyone wants is to do a 301 in a domain with numerous spam or porn links to a perfect domain. If the domains appear to have signs of unlawful activities in the past, avoid 301 redirecting it to the main domain.
Nevertheless, if the domains in question present type-in value, you can 302 redirect them to the website. Also, you need to check Google for an actively ranking page on the domains. If such pages rank, is the existing content in line with the current content? There is no need to redirect a domain that ranks in basketball jerseys to a domain that sells guns. If you notice that the website might be hacked (from the SERPs), you can still use the domain, but you will have to obliterate the entire database and file system connected to the website. You also can move the hosting environment if there are essential features associated with the domain (like directly related content, great backlinks, etc.).
Avoid having Websites that Answer to Multiple Domains
You can redirect multiple domains to the client's website; however, avoid creating multiple identical content websites.
On Domains, the client needs you to redirect to their website, run due checks on them
Backlink History: Does the website checkout as 'clean'? If the site was undesirable in the past, don't redirect it to the client's website.
Prior content: If the existing content on the domain is not directly related to the current website, most likely no value is present there.
Don't redirect compromised or hacked domains.
Do the Domains have the needed type-in value?
Redirect if an undesirable domain has a promising type-in potential.
If the client initially registered some domains similar to those in question, you don't need to make these known at the client's website, for instance, if they possess the same name and TLD domain.
In summary, getting value in this strategy ultimately depends on the domains you are checking out and how they relate to the existing content.