/**
 * SMTP mailbox probe.
 *
 * Walks `mxRecords` in priority order, then `ports` in the configured order.
 * Returns the first attempt that yields a definitive answer (250 / 550 / 552 /
 * 452); on indeterminate outcomes (timeouts, connection resets, EHLO failures,
 * unrecognized responses), falls through to the next MX×port pair.
 *
 * Per-attempt dialogue:
 *   greeting → EHLO → MAIL FROM → RCPT TO real → RCPT TO probe → RSET
 *
 * The probe RCPT uses a guaranteed-nonexistent random local-part so we can
 * detect catch-all MXes (Outlook / Yahoo / Office 365 / ProtonMail / many
 * corporates accept every recipient at the MX layer and bounce later).
 * When both real + probe return 250, `result.isCatchAll = true` and callers
 * know the deliverability signal is unreliable but that the address syntax
 * was at least accepted.
 *
 * The envelope (real RCPT + probe RCPT + RSET) is batched via PIPELINING
 * (RFC 2920) when the MX advertises support — roughly halves wire-level
 * latency. Tests can disable with `pipelining: 'never'` for deterministic
 * `socket.write()` call counts.
 *
 * Every result carries a `metrics` block with `mxAttempts`, `portAttempts`,
 * `mxHostsTried`, `mxHostUsed?`, `totalDurationMs` — useful for region-health
 * dashboards and root-cause-analysis when probes go wrong.
 */
import type { SmtpVerificationResult, VerifyMailboxSMTPParams } from './types';
export interface ParsedDsn {
    /** 2 = success, 4 = transient, 5 = permanent */
    class: number;
    /** 1 addressing, 2 mailbox, 3 mail-system, 4 network, 5 protocol, 6 message, 7 security/policy */
    subject: number;
    detail: number;
}
/**
 * Parse an RFC 3463 enhanced status code at the start of an SMTP reply.
 * Examples: "550 5.1.1 user unknown" → {5,1,1}; "421 4.7.0 try later" → {4,7,0}.
 */
export declare function parseDsn(reply: string): ParsedDsn | null;
/**
 * Public entry point. Walks `mxRecords × ports` and returns the first
 * definitive answer. Always:
 *   - iterates MX records on indeterminate outcomes (no flag)
 *   - runs the catch-all dual-probe (no flag)
 *   - populates `result.metrics` and `result.enhancedStatus`
 *
 * Opt-in only:
 *   - `captureTranscript: true` returns the wire transcript on the result
 *   - `pipelining: 'never'` disables PIPELINING for deterministic tests
 *   - `catchAllProbeLocal` overrides the random-local generator
 */
export declare function verifyMailboxSMTP(params: VerifyMailboxSMTPParams): Promise<{
    smtpResult: SmtpVerificationResult;
    cached: boolean;
    port: number;
    portCached: boolean;
}>;