Internet Address?
Internet addresses can be case sensitive — it depends on the system
addressed and the system you send from. Some (few) mail systems convert
everything to upper (or lower) case. Some mail systems have
case-sensitive user names (and hence user-parts of addresses).
In general, I write everything in lowercase unless the address I have been
given has a user name in mixed case or the address uses a gateway to route
through a non-Internet machine.
— Dale L. Larson, Intangible Assets Manufacturing
— INTERNET:dale@iam.com