How to handle the 301 of a complete domain on URL level

[Windex]

We will be shutting down an old website with many (good) links, since the site has no strategic relevance anymore. We do have many other sites, but none of them has exactly the same content/topic. Nonetheless, I would like to keep the juice and redirect the site to another newer project. However, I want to redirect certain URLs of the old site to probably even different domains, depending on which content matches best with the alternative newer site. Does this make sense? Or would youjust redirect the whole domain to one other domain although they don't really have the same topic

And how would you handle the URL redirects if the old site has more than 50k URLs? Because that is the case.

Thanks for any advice

[netsites]

I would do page-to-page 301 redirects to the webpages with topics that are most closely relevant to the old webpages' topics. Yes, you can do page-to-page redirects to webpages with different domain names.  It's going to take a lot of work if you have to do that with 50k URLs though!

I suggest that you consider this:  Keep hosting it and replace the main page's content with a paragraph explaining that the website is on pause. It can contain a link to some of your other websites.

Here's why I suggest that:  I have a client with a website with a Google PageRank of 3.  He closed the business and wanted to ditch the website since he was starting a new biz.  Instead, he let me put up a blank page with a paragraph stating that the business was closed. And I reduced my hosting fee for that website. There were no longer any internal links to the inner webpages, other than on the sitemap.xml.  Nearly six months later, the website still has maintained Google PR3 (and PR2 for inner pages), and someone has approached him wanting to buy the website!  Yay!

One last idea:  You could contact the websites that link to the soon-to-be-retired website and ask them to link instead to one of your other, relevant websites. Hope this helps!  Good luck!