Hi Bob,
There are all kinds of things crawling the web that will mangle together urls on your site and try them. I get this kind of thing in my logs daily but it does not correspond to normal user traffic, no-one has ever reported broken links with such urls and nowhere in mojoportal code do we surface links with those incorrect urls.
If you are getting emails about every exception that must be something you setup yourself, we just log it under Administration > System Log, maybe you setup an smtp logger for log4net, but I don't know a way to make it filter out specific errors, it will log all unhandled errors and also some handled errors. A 404 (Page Not Found) is a handled error but we need to log it in case we ever do have broken urls we can find them, but these specific url errors are not from real urls in the site so you should ignore them.
Hope it helps,
Joe