@sdxc/email-address

Email address parsing and normalization, disposable-domain detection, and mail-server checks.

Installation

npm add @sdxc/email-address

Checks return @sdxc/result values; install it alongside to narrow them with isFailure and isSuccess.

Usage

Parse An Address

import { parseEmailAddress } from "@sdxc/email-address";
import { isSuccess } from "@sdxc/result";

let parsed = parseEmailAddress("  Jane.Doe@Bücher.Example ");

if (isSuccess(parsed)) parsed.data;
// {
//   address: "Jane.Doe@xn--bcher-kva.example",
//   canonical: "jane.doe@xn--bcher-kva.example",
//   localPart: "Jane.Doe",
//   domain: "xn--bcher-kva.example",
// }
else parsed.error.reason; // "local-part-invalid", "domain-invalid", …

Refuse A Disposable Address

import type { EmailAddress } from "@sdxc/email-address";

import { checkDisposable } from "@sdxc/email-address/disposable";

function refuseDisposable(address: EmailAddress) {
	return checkDisposable(address); // failure for jane@inbox.mailinator.com
}

Check The Domain Receives Mail

import { checkMailServer } from "@sdxc/email-address/mail-server";

let servers = await checkMailServer("example.com");
// success({ domain: "example.com", hosts: ["mx1.example.com"], implicit: false, ttl: 300 })

Suggest A Fix For A Mistyped Provider

import type { EmailAddress } from "@sdxc/email-address";

import { suggestDomain } from "@sdxc/email-address/typo";

function didYouMean(address: EmailAddress) {
	return suggestDomain(address)?.address; // "jane@gmail.com" for jane@gmial.com
}

API

Each capability has its own export path, so code that only parses bundles neither the ~130 KB disposable-domain list nor the DNS client. Every failure carries a reason code, so an app maps each one to its own message.

@sdxc/email-address

parseEmailAddress(input): Result<EmailAddress, InvalidEmailAddressError>

NFKC-normalizes and trims the input, splits it at the last @, and accepts an RFC 5322 dot-atom local part (plus non-ASCII per RFC 6531, except controls, invisible format characters, unassigned and private-use code points, and spaces) of at most 64 UTF-8 octets. Quoted local parts ("jane doe"@example.com) are refused. The domain follows normalizeDomain, and the whole address is at most 254 octets (RFC 5321).

An EmailAddress holds:

• address - the local part as entered, @, and the ASCII domain. Store and send to this one: RFC 5321 lets a mail host treat local-part case as significant.

• canonical - address with the local part lowercased. Key uniqueness and lookups on this one. Dots and +tags stay: only the mail host knows whether j.ane+news@ and jane@ share a mailbox, and a wrong guess merges two people.

• localPart - NFKC-normalized, case as entered.

• domain - lowercased and ASCII-encoded (punycode), the form DNS and SMTP use.

normalizeDomain(input): Result<string, InvalidEmailAddressError>

The domain rule on its own, for a bare domain such as one an organization claims. The input is NFKC-normalized and trimmed, any ASCII besides letters, digits, - and . is refused, and the rest is IDNA-encoded the way the URL standard parses a host. The result needs at least two labels of 1–63 letters, digits and inner hyphens, at most 253 characters, and a top-level label that is not all digits, so IP literals, single-label names (localhost) and a trailing root dot (example.com.) are refused.

normalizeDomain("Straße.DE"); // success("xn--strae-oqa.de")

InvalidEmailAddressError

The failure of both functions. reason is one of:

EmailAddress and EmailAddressReason are exported as types.

@sdxc/email-address/disposable

The bundled list is the disposable-email-domains blocklist, dedicated to the public domain under CC0-1.0 and taken on 2026-09-27. A domain matches when it equals a listed domain or is a subdomain of one: x.mailinator.com matches mailinator.com. To accept a listed domain anyway, test for it before calling checkDisposable.

checkDisposable(address): Result<EmailAddress, DisposableDomainError>

Passes the address through unchanged, or fails with a DisposableDomainError whose reason is "disposable-domain" and whose domain is the listed entry it matched.

isDisposableDomain(domain): boolean / findDisposableDomain(domain): string | null

Whether an ASCII domain is listed, or which entry it matched. Case and one trailing dot are ignored; pass an internationalized domain in its ASCII form, as normalizeDomain returns it.

@sdxc/email-address/mail-server

checkMailServer(domain, options?): Promise<Result<MailServers, MailServerError>>

Checks that an ASCII domain can receive mail, the way a sending server finds its hosts, over DNS over HTTPS through @sdxc/doh. options go to each lookup: resolver (Cloudflare by default), timeoutMs (default 5000), signal, dnssec and checkingDisabled.

MailServers holds domain, hosts, implicit, and ttl, the smallest TTL among the records the answer rests on (null when none reported one). MailServerError holds reason and, for domain-not-found and lookup-failed, the DNS error as cause. MailServerReason is exported as a type.

This proves the domain can receive mail, never that the mailbox exists: that takes an SMTP conversation, which serverless runtimes cannot open and which gets the prober blocklisted. Confirm a mailbox by sending it a link or code.

@sdxc/email-address/role-account

checkRoleAccount(address): Result<EmailAddress, RoleAccountError>

Fails with a RoleAccountError whose reason is "role-account" and whose role is the match when the local part, lowercased and with any +tag removed, names a function rather than a person: abuse, admin, administrator, billing, contact, do-not-reply, donotreply, ftp, help, hostmaster, info, mailer-daemon, marketing, news, no-reply, noc, noreply, postmaster, root, sales, security, support, sysadmin, usenet, uucp, webmaster, www. Only the whole local part counts, so sales-jane@ passes.

@sdxc/email-address/typo

suggestDomain(address): EmailAddress | null

The address with its domain replaced by the provider it most likely meant, or null. The providers are gmail.com, yahoo.com, hotmail.com, outlook.com, icloud.com, googlemail.com, protonmail.com, yandex.com and fastmail.com. A domain one edit away (insert, delete, substitute, swap two adjacent letters) is corrected, or two edits away for providers of ten characters or more; mail.com, email.com and ymail.com get no suggestion.

Pattern: Validate A Sign-Up Address

Parse first, run the checks that need no network, then the DNS check, and decide what an unknown answer means.

import { parseEmailAddress } from "@sdxc/email-address";
import { checkDisposable } from "@sdxc/email-address/disposable";
import { checkMailServer } from "@sdxc/email-address/mail-server";
import { suggestDomain } from "@sdxc/email-address/typo";
import { isFailure } from "@sdxc/result";

async function validateSignUpEmail(input: string) {
	let parsed = parseEmailAddress(input);
	if (isFailure(parsed)) return { error: parsed.error.reason };

	let suggestion = suggestDomain(parsed.data)?.address;

	let disposable = checkDisposable(parsed.data);
	if (isFailure(disposable)) return { error: disposable.error.reason };

	let servers = await checkMailServer(parsed.data.domain, { timeoutMs: 2000 });
	if (isFailure(servers) && servers.error.reason !== "lookup-failed") {
		return { error: servers.error.reason, suggestion };
	}

	return { email: parsed.data, suggestion };
}

lookup-failed fails open here: a resolver outage never blocks a sign-up, and the confirmation email is the real test. Fail closed instead where a bad address costs more than a lost sign-up.

Pattern: Store One Form, Index The Other

Keep address for sending and a unique index on canonical, so a second sign-up with different capitalization finds the existing account.

import { parseEmailAddress } from "@sdxc/email-address";
import { isFailure } from "@sdxc/result";

interface Users {
	findByCanonicalEmail(canonical: string): Promise<{ id: string } | null>;
	create(user: { email: string; emailCanonical: string }): Promise<{ id: string }>;
}

async function findOrCreateUser(users: Users, input: string) {
	let parsed = parseEmailAddress(input);
	if (isFailure(parsed)) return parsed;

	let existing = await users.findByCanonicalEmail(parsed.data.canonical);
	return (
		existing ?? users.create({ email: parsed.data.address, emailCanonical: parsed.data.canonical })
	);
}

Pattern: Cache Mail-Server Answers

A burst of sign-ups from one domain costs one lookup when the answer is cached for its ttl.

import type { MailServers } from "@sdxc/email-address/mail-server";

import { checkMailServer } from "@sdxc/email-address/mail-server";
import { isSuccess } from "@sdxc/result";

let cache = new Map<string, { servers: MailServers; expires: number }>();

async function mailServersFor(domain: string) {
	let cached = cache.get(domain);
	if (cached && cached.expires > Date.now()) return cached.servers;

	let servers = await checkMailServer(domain);
	if (!isSuccess(servers)) return null;

	let seconds = Math.max(servers.data.ttl ?? 300, 60);
	cache.set(domain, { servers: servers.data, expires: Date.now() + seconds * 1000 });
	return servers.data;
}