/**
 * Return `subject` with an `Re: ` prefix added unless one already exists.
 * Matches `Re:`, `RE:`, `re:`, `Re :` etc. — but not non-reply strings like
 * "Are: the books ready" where `includes("Re:")` would give a false positive.
 */
export declare function ensureReplyPrefix(subject: string): string;
/**
 * Return `subject` with a `Fwd: ` prefix added unless one already exists.
 * Accepts the common variants `Fwd:`, `Fw:`, `FWD:`, case-insensitive.
 */
export declare function ensureForwardPrefix(subject: string): string;
/**
 * Pull the bare addr-spec out of a header value, so `Name <user@example.com>` and
 * `user@example.com` both compare equal. Lowercased because mail domains are
 * case-insensitive and alias lists are matched by equality.
 */
export declare function extractAddress(raw: string): string;
export declare function strictAddress(raw: string): string | null;
/**
 * Split a header value like `"Smith, John" <j@x>, Other <o@y>` into the
 * individual address strings. Commas inside double-quoted display names or
 * inside angle brackets are preserved.
 */
export declare function splitAddressList(raw: string): string[];