/**
 * Minimal SMTP submission client over an injectable transport socket.
 *
 * Scope and honest boundaries
 * ────────────────────────────
 * Supported:
 *   - EHLO negotiation
 *   - AUTH PLAIN and AUTH LOGIN
 *   - MAIL FROM / RCPT TO / DATA with RFC 2821 dot-stuffing
 *   - A generated RFC 5322 `Message-ID` on every send, returned to the caller
 *     along with the moment the server accepted the message
 *   - QUIT
 *   - TLS-direct (port 465) via `createSmtpTlsSocket()`
 *   - STARTTLS upgrade (port 587) via `createSmtpStartTlsSocket()`
 *
 * Not supported (document boundaries):
 *   - HTML, MIME multipart, attachments
 *   - Multiple recipients in a single session (call sendMail per recipient)
 *   - DSN / delivery-status-notification extensions
 *   - PIPELINING (all commands are sent sequentially and await a reply)
 *   - Credentials are never logged
 *
 * Transport injection
 * ────────────────────
 * The `socket` parameter accepts any net.Socket so that unit tests can supply
 * a plain in-process fake socket instead of a real TLS connection. Both socket
 * factories named above live in the sibling `email/node` entry, so importing
 * this module never opens a connection or pulls `node:tls` in behind it.
 */
import type { Socket } from 'node:net';
export interface SmtpClientOptions {
    readonly socket: Socket;
    readonly hostname: string;
    readonly username: string;
    readonly password: string;
    readonly timeoutMs?: number;
}
export interface SmtpSendOptions {
    readonly from: string;
    readonly to: string;
    readonly subject: string;
    readonly body: string;
}
/** What a completed send is afterwards identifiable by. */
export interface SmtpSendResult {
    /**
     * The `Message-ID` header this send actually carried, angle brackets
     * included. It is generated here, written into the message, and handed back
     *, the same string on the wire and in the return value, because its whole
     * purpose is to correlate with what left the machine and with the
     * `In-Reply-To` of whatever comes back.
     */
    readonly messageId: string;
    /**
     * ISO-8601 instant the server ACCEPTED the message, read after the final
     * `250`, not when the attempt started, so it records a send that happened
     * rather than one that was tried.
     */
    readonly sentAt: string;
}
/** Per-operation timeout, and the connect timeout used by the node adapter. */
export declare const SMTP_DEFAULT_TIMEOUT_MS = 15000;
/**
 * Validate a single SMTP envelope address (MAIL FROM / RCPT TO value).
 * Rejects: control characters (\r, \n, any C0 or C1), spaces, angle brackets,
 * comma-separated lists. Only a single bare address is accepted.
 *
 * @throws Error with a plain-language message on invalid input.
 */
export declare function validateSmtpAddress(address: string, field: string): void;
/**
 * Validate an SMTP message Subject header value.
 * Rejects control characters (\r, \n, etc.) that could split headers.
 *
 * @throws Error with a plain-language message on invalid input.
 */
export declare function validateSmtpSubject(subject: string): void;
export declare class SmtpClient {
    private readonly options;
    constructor(options: SmtpClientOptions);
    /**
     * Connect, negotiate EHLO, and authenticate, then QUIT without sending any
     * mail. Used to verify SMTP credentials/host reachability (a connect-wizard
     * "test connection" step) without the side effect of an actual send.
     * Throws with a plain-language message on any failure stage.
     */
    verifyAuth(): Promise<void>;
    /**
     * Send a plain-text email.
     * Callers must ensure the caller-side confirms the send before calling this.
     *
     * Returns the `Message-ID` the message actually carried and the instant the
     * server accepted it. Nothing about either value is invented after the fact:
     * the id is written into the headers that go out, and the timestamp is read
     * once the final `250` has arrived.
     */
    sendMail(opts: SmtpSendOptions): Promise<SmtpSendResult>;
    /** Read the server greeting and negotiate EHLO. Shared by sendMail and verifyAuth. */
    private greetAndEhlo;
    private authenticate;
}
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