404 handler and dynamic pages that really don't exists... bad for SEO?

We have an IIS 404 asp.net handler that renders pages when an html page is not found. It uses the page's URL to query our Databases and builds rich relevant content on the fly. From what I can tell in the IIS logs and anaylyzing the pages from web browser tools there is NO indication the page does not actually exist and was dynamically generated.

In these cases is IIS actually sending a 404 to the client? Is there a redirect of any kind actually happening? Will Search engines punish me for this?

It's been 2 months and Google has indexed everything, but Bing and Yahoo have not indexed anything dynamic dispite my submitting various Directory pages, Sitemaps and Feeds with all my links. My home page is indexed on all search engines and has all my links. When I search very unique keywords in those links, I can see that bing and yahoo do see them on my Home Page links - but only there.

Is there anything I can run or check to make sure my dynamic pages are not somehow viewed as 开发者_StackOverflowbad by Search engines? Any way to check if a 404 (whatever a 404 actually is to a client besides just another page) is returned to crawlers?

Many Thanks.

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Is there anything I can run or check to make sure my dynamic pages are not somehow viewed as bad by Search engines?

Dynamic pages are just fine. Most of the content on the Internet is dynamically produced. The search engines don't care if content is dynamic and, in fact, they usually do not know content is dynamic as all they see if the URL and the HTML that is produced by that URL.

Any way to check if a 404 (whatever a 404 actually is to a client besides just another page) is returned to crawlers?

Use a tool like Firebug or the built in developer tools in Chrome to view your HTTP headers. Crawlers see the same headers a browser would see so that is an easy way to tell what headers your pages are sending out.