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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesA Node.js email check should distinguish three outcomes: invalid when an address fails your documented syntax policy, domain mail route found when syntax passes and DNS returns usable mail-routing evidence, and unknown when checks cannot support a reliable conclusion. An MX record says something about routing for a domain; it does not prove that a particular mailbox exists or will accept a message.
What the three states mean
Keep syntax acceptance separate from domain-level routing. A parser can decide whether an input fits the address forms your application accepts. A DNS lookup can report mail-exchanger records for the domain. Neither check, alone or together, verifies the local-part—the text before @—against a recipient mailbox.
| State | Use it when | What it does not mean |
|---|---|---|
invalid |
The input fails your documented input policy or parser. | It is not a conclusion drawn merely from a DNS error. |
domain_mail_route_found |
Syntax passes and the domain has usable MX evidence under your policy. | It does not establish that the mailbox exists or that delivery will succeed. |
unknown |
A DNS failure, timeout, ambiguous DNS outcome, unsupported form, or unavailable check prevents a firm classification. | It is not another word for invalid. |
SMTP explicitly recognizes that an address can appear valid yet not be reasonably verifiable in real time. RFC 5321 describes such cases, including when a server relays for another server or domain. Remote-server policy and behavior can also affect acceptance. For that reason, treat this gate as a screening aid, not proof of deliverability. RFC 5321
Choose and document your syntax policy
For ordinary signup forms
If your product intentionally accepts only a practical subset of internet addresses, document that policy and use a maintained parser or carefully scoped validation library. Avoid claiming that one hand-written regular expression implements the complete email-address standards. Narrow rules can reject legitimate, less common forms.
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For broader compatibility
Quoted local-parts, address literals, internationalized addresses, and differences between envelope and header formats complicate parsing. RFC 3696 says quoted forms are uncommon but must be supported by applications processing user-provided addresses. It states historical length limits of 64 octets for the local-part and 255 octets for the domain part; those are octet figures from the 2004 RFC, not JavaScript character-count rules for every internationalized address. RFC 3696
One possible library is Haraka’s @haraka/email-address. Its project documentation describes envelope and header parsing, quoted local-parts, address literals, internationalized addresses, and ESM/CommonJS entry points. Review its supported input flavor, current version, and maintenance status against your own product requirements before adopting it; those project features are not an independent assessment.
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Resolve MX records with Node.js
Node.js exposes resolveMx(domain) from node:dns/promises. A successful result is an array of records containing priority and exchange. This is a domain-level DNS query, not a mailbox lookup. The implementation below shows the outcome shape and deliberately leaves policy decisions—especially DNS edge cases—to your application. Node.js v26.10.0 DNS API documentation
import { resolveMx } from 'node:dns/promises';
async function assessEmail(input) {
const parsed = parseUnderYourDocumentedPolicy(input);
if (!parsed.ok) {
return { status: 'invalid', reason: 'syntax' };
}
try {
const records = await resolveMx(parsed.domain);
if (records.length === 0) {
return { status: 'unknown', reason: 'no-mx-result' };
}
return {
status: 'domain_mail_route_found',
signal: 'mx-records-found',
mx: records.map(({ priority, exchange }) => ({ priority, exchange }))
};
} catch (error) {
return { status: 'unknown', reason: 'dns-query-inconclusive' };
}
}parseUnderYourDocumentedPolicy is an application-specific placeholder, not a Node.js API. Supply it with a real parser and ensure it returns a normalized domain only when the input passes your chosen policy. The example is illustrative, not tested production code.
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Define DNS outcomes before using them
A successful MX lookup with usable records supports the narrow claim “mail exchanger records found.” Other DNS results need deliberate handling. RFC 5321 permits resolvable fully qualified domain names through MX records or address records, while resolveMx specifically retrieves MX records. A policy that interprets an empty MX result as invalid may therefore reject domains whose mail routing is established differently.
- Usable MX records: return
domain_mail_route_foundif syntax passed and your policy considers the records usable. - No MX records or explicit non-mail configuration: do not automatically treat an empty result as proof that the submitted mailbox is invalid. Decide whether address-record fallback is within scope; otherwise return
unknown. - Resolver error or timeout: return
unknown, notinvalid. The lookup did not establish the address’s status. - Transient or ambiguous result: preserve
unknownand, if appropriate, allow a retry or later verification rather than making a permanent user-level judgment.
Node’s documented MX resolver provides the lookup mechanism; it does not choose your product’s fallback, timeout, or retry policy. Set those choices to match the risk of the action being gated.
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Choose what your application does with unknown
Make the outcome useful to the caller instead of forcing every check into a binary boolean. For a low-friction signup, one reasonable policy is to allow account creation and require email confirmation before enabling sensitive actions. A contact form might accept the submission while flagging the address for follow-up. A higher-risk workflow may defer the decision until another verification step. The appropriate action depends on the consequences of a false acceptance or rejection; DNS uncertainty alone is not evidence that a user entered a bad address.
Keep the result name and user-facing message precise. “Syntax accepted” describes the parser result; “mail exchanger records found” describes the DNS signal. Reserve “mailbox exists,” “deliverable,” and “guaranteed valid” for evidence these checks do not provide.
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| Approach | Best fit | Trade-offs to assess |
|---|---|---|
| Narrow application syntax policy plus Node.js MX lookup | A simple flow accepting ordinary internet addresses. | Accepted forms, false-rejection risk, lookup latency, DNS failure handling, and explicit unknown behavior. |
| Standards-oriented parser plus Node.js MX lookup | Products that need quoted or legacy forms, address literals, internationalized cases, or multiple syntax contexts. | Supported grammar, envelope versus header mode, package maintenance, performance needs, and product policy. |
The parser project documents its own performance characterization, but that is not an independent benchmark. Select a parser based on the grammar and maintenance you need, and measure performance in your own application if it matters.
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