A CNAME record is an abbreviation for Canonical Name record and is a type of resource record in the Domain Name System (DNS) that specifies that the domain name is an alias of another, canonical domain name.
You have to figure out for yourself how to set such a record with your own DNS provider but here are the details:
Have your CNAME record point to dl.dropbox.com.
Now, every time you acquire a link to share a public dropbox ressource and your request is blocked by some entity in your network, you can exchange the host to use a different, hopefully unfiltered domain name and still access that file.
In this example the following link to my public resume looks like this:
The modified version will look like this:
Note that you would need to give up HTTPS security for this to work because the security certificate served by the dropbox download servers obviously states a different host name. 02/06/2013