Solution: Store emails with case sensitivity Send emails with case sensitivity Perform internal searches with case insensitivity

Robustness principle suggests that we accept case sensitive emails

You should default to the most permissive option imo and there really is no reason to check anything until you really need to If it were left to me I'd just use optional chaining, as it also eliminates the need for no-ops

In other words, programs that send messages to other machines (or to other programs on the same machine) should conform completely to the specifications, but programs that receive messages should accept non-conformant input as long as the meaning is clear.

be conservative in what you do, be liberal in what you accept from others