isValidEmail

Returns true if this String looks like a valid email address.

This is a pragmatic, permissive check rather than a full RFC 5322 implementation: it accepts the common local-part characters (letters, digits, and ._%+-, so plus-addressing works), single-character domain labels, modern long TLDs, and bare IPv4-literal domains. It does not accept quoted local parts, internationalized (Unicode) domains, or bracketed/IPv6 address literals.

Addresses longer than 254 characters, or with a local part longer than 64, are rejected before the pattern runs (RFC 5321's limits). That also bounds the regex engine's recursion, which grows with the number of domain labels, so untrusted input cannot overflow the stack.