One of the best ways to use expired domains for your SEO is to use broken link building. This white hat method of gaining backlinks to your website can take a lot of time due to outreach, but requires the least monetary investment.
First, you need to identify an expired domain in your niche that has a range of high-quality backlinks to steal broken links.
Next, you need to reach out to the websites that link to the expired domain and inform them of the broken link. Then offer them an alternative resource to link to on your site to replace the broken link.
The email should look something like this: