It’s important to go back through your website and search it out for items that might be a red flag for the search engines. That might mean creating a new sitemap once in a while.
Duane Forrester of Bing says as much in an interview conducted late last year.
Your Sitemaps need to be clean. We have a 1% allowance for dirt in a Sitemap. Examples of dirt are if we click on a URL and we see a redirect, a 404 or a 500 code. If we see more than a 1% level of dirt, we begin losing trust in the Sitemap.
In other words, if you have a website with 20 pages on it and you have 2 of those pages with 301 redirects, 1 with a 404 error, and 1 that returns a constant 500 error, then your sitemap could be killing your search rankings in Bing.
A 500 error usually refers to some kind of server issue. It’s not likely that you’ll get a 500 error on one page and not on another, but it could happen. If you recently changed permissions on one page of your website and failed to change it back to the original permissions setting, then that page could turn a 500 error.
A 404 error means that the server couldn’t find your page. There is likely something wrong with the permalink in your sitemap.
All of this is simply to say that you should present a clean sitemap to the search engines if you expect them to honor it. If it’s been a while since you’ve created your 301 redirects, use the rel=canonical tag and delete those pages from your server. You can then also delete the redirects from the sitemap. But make sure those pages are not indexed in the search engines first.
And of course you want to fix any errors as well – 404s, 500s, etc. Fix the errors and reduce the number of 301 redirects in your sitemap. Keep it clean.