On: foo@bar.com

[djsumdog]

I always used bob@bob.bob. It's not a real TLD (although at the rate of new TLDs, it might be soon) but it still validated on most websites.

[JdeBP → djsumdog]

Someone whimsical will grab it, and not be happy with the ground that you've laid. Consider that dot@dotat.at exists.

* https://news.ycombinator.com/item?id=21369013

[Xylakant → JdeBP]

Though it is substantially easier to register a domain for fun than register a TLD for fun, even though the principle remains the same: pay some money and do some DNS configuring. It’s just that for TLDs the value of “some” changes.