Forward using CNAME record

[Henry Hartley]

My apologies if this gets to the list twice. I tried to post it through 
the web interface but it seems to have been dropped by whatever 
screening gets applied.

I'm not sure if I've misunderstood the use of CNAME or if I've simply 
done something wrong.

I have two domains that I want to forward. One is working properly and 
the other is not. In both cases I want users to enter a URL in their 
browser (www.example.com) and be forwarded to a different system, where 
the user has their site. In the working case, the forwarding it to 
web.me.com so I have the following in my zone file:

www.example.com.   CNAME   web.me.com.

When you point your browser to www.example.com (obviously not
"example") the page on web.me.com loads properly but www.example.com is 
still displayed in the address bar.

In the second case, which is NOT working, I have a similar CNAME record 
but instead of web.me.com, it's on tumblr.com. So, I have this (this is 
the actual domain):

www.ioanamorosan.com.  CNAME   ioanamorosan.tumblr.com.

If you go directly to ioanamorosan.tumblr.com, the site loads, but if 
you go to www.ioanamorosan.com, you get a tumblr.com 404 error page. The 
browser still displays www.ioanamorosan.com in the address bar.

So, is this a situation where web.me.com is set up to recognize 
www.example.com properly but tumblr.com is not? Or what?

Should I be able to do what I'm trying to do?

--
Henry