/**
* RFC 6376 (RSA-SHA256) + RFC 8463 (Ed25519-SHA256) DKIM signer.
*
* Ships relaxed/relaxed canonicalization because it's what gmail,
* yahoo, outlook and every popular mail server prefer in 2026. Uses
* Web Crypto throughout — no node:crypto — so the SMTP driver can run
* on Cloudflare Workers if you bring your own socket transport.
*
* @module
*/
export interface DkimSignerOptions {
	/** DNS selector — the TXT record at `<selector>._domainkey.<domain>`. */
	selector: string;
	/** Signing domain. */
	domain: string;
	/** Private key as PEM (RSA: PKCS8 or PKCS1; Ed25519: PKCS8). Also
	*  accepts a pre-imported CryptoKey. */
	privateKey: string | CryptoKey;
	/** Signing algorithm. Default: `rsa-sha256`. */
	algorithm?: "rsa-sha256" | "ed25519-sha256";
	/** Headers to include in the signature. Default set is the canonical
	*  minimal list recommended by RFC 6376. */
	headers?: ReadonlyArray<string>;
}
/** Per-message signer. Takes a built RFC 5322 message (headers + CRLF +
*  body) and returns a new message with a leading `DKIM-Signature:`
*  header. */
export declare function signDkim(message: string, options: DkimSignerOptions): Promise<string>;