Normalises and validates an email address (trim + lower-case). Deliberately conservative: it rejects
anything with whitespace, control characters, quotes, angle brackets or a display-name form, because
the address is about to be placed in a message header and a link context.
Normalises and validates an email address (trim + lower-case). Deliberately conservative: it rejects anything with whitespace, control characters, quotes, angle brackets or a display-name form, because the address is about to be placed in a message header and a link context.