/**
 * @module
 * SMTP connection pool with optional rate limiting.
 *
 * @example
 * ```ts
 * import { SMTPPool } from "sently/pool";
 * import { NodeAdapter } from "sently/adapters/node";
 *
 * const pool = new SMTPPool({
 *   host: "smtp.example.com",
 *   auth: { user: "you@example.com", pass: "secret" },
 *   adapter: new NodeAdapter(),
 *   pool: true,
 *   maxConnections: 5,
 * });
 *
 * await pool.send({
 *   from: "you@example.com",
 *   to: "recipient@example.com",
 *   subject: "Hello",
 *   text: "Pooled send",
 * });
 * ```
 */
import type { MailOptions, PoolConfig, SendResult, SMTPConfig, SocketAdapter, Transport, VerifyResult } from "../core/types.js";
/** Options for {@link SMTPPool}. */
export interface SMTPPoolOptions {
    /** Factory for a new socket adapter per pooled connection. */
    createAdapter?: () => Promise<SocketAdapter> | SocketAdapter;
    /** Injectable clock for rate limiting (testing). */
    now?: () => number;
}
/**
 * SMTP connection pool with optional rate limiting.
 */
export declare class SMTPPool implements Transport {
    /** Resolved SMTP and pool configuration. */
    private readonly config;
    /** Maximum simultaneous pooled connections. */
    private readonly maxConnections;
    /** Maximum messages per connection before recycle. */
    private readonly maxMessages;
    /** Factory that creates a socket adapter for each new connection. */
    private readonly createAdapterFn;
    /** Optional token-bucket rate limiter, or null when disabled. */
    private readonly rateLimiter;
    /** Active pooled SMTP connections. */
    private readonly connections;
    /** Pending send operations waiting for a connection. */
    private readonly queue;
    /** True while {@link close} is draining; rejects new sends. */
    private draining;
    /** True after the pool has fully closed. */
    private closed;
    /** Serializes queue processing to avoid concurrent drain races. */
    private processChain;
    /** Creates an SMTP connection pool. */
    constructor(config: SMTPConfig & PoolConfig, options?: SMTPPoolOptions);
    /** Sends a message through the pool. */
    send(options: MailOptions): Promise<SendResult>;
    /** Schedules asynchronous processing of the send queue. */
    private scheduleProcess;
    /** Verifies connectivity using a temporary connection. */
    verify(): Promise<VerifyResult>;
    /** Drains the queue and closes all connections. */
    close(): Promise<void>;
    /** Current number of open pooled connections. */
    get connectionCount(): number;
    /** Number of messages waiting in the send queue. */
    get queueSize(): number;
    /** Dispatches queued messages to idle or newly spawned connections. */
    private processQueue;
    /** Opens a new authenticated pooled SMTP connection. */
    private spawnConnection;
    /** Removes a connection from the active pool list. */
    private removeConnection;
    /** Waits until the send queue and in-flight work are fully drained. */
    private drainQueue;
}
/** @internal Exposed for deterministic rate limiter tests. */
export { RateLimiter } from "../core/rate-limiter.js";