[cbd1984]

JANET, which routed email to Czechoslovakia, as the legend goes...

Back then mainly the Computer Science departments had email, so they'd have domain names beginning with a cs. in the ARPA scheme, but, since JANET did it backwards, you'd have to rearrange the domain name so it ended with a .cs for that network. If you did that and didn't reverse it back, the domain name would have a ccTLD of .cs, which is what Czechoslovakia used.

(The .cs ccTLD existed until 1995, years after Czechoslovakia ceased to. The .su ccTLD (Soviet Union) still exists.)