Our bulk email validation service runs 16 static checks on every address: RFC 5321 envelope syntax, DNS and MX lookups, reserved TLD rules, disposable and role filters, gibberish scoring, and Levenshtein typo correction. It is the first of two layers in our bulk email verification service, running before the SMTP verifier. 99.7% accuracy across the full pipeline.
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Create AccountTogether they make up our bulk email verification service. The validator handles the static layer first, and only the addresses that pass continue into the verifier for the live SMTP check. Anything the validator rejects never reaches the verifier.
Every address is checked against RFC 5321 envelope syntax, DNS and MX records, reserved TLD rules per RFC 2606 and 6761, and our intelligence datasets: disposable, role, free email provider, gibberish, and typo correction.
No connection to the destination mail server at this layer. Fast, cheap, deterministic. Catches roughly 10 to 15 percent of bad addresses on typical lists (up to 20 percent on older, stale lists) before the verifier layer runs.
Opens a TCP connection to the destination mail server and confirms the specific mailbox exists via an SMTP RCPT TO probe. No message is ever sent.
Handles catch-all detection, greylisting retry, and reply-code verdict mapping. The authoritative answer on mailbox existence and the second half of the same bulk email verification service.
See the bulk email verificationEvery address moves left-to-right through these four validation layers. Each layer filters, annotates, or normalizes before the next runs. Addresses that pass all four are handed to the SMTP verifier layer, documented on the bulk email verification page.
Trim whitespace. Lowercase the domain portion. Collapse duplicates. Reject anything that cannot be parsed as an address.
trim · lowercase · dedupEnforce RFC 5321 envelope rules. Length limits, reserved characters, and domain label rules.
RFC 5321 · 5233Authoritative MX lookup. A or AAAA fallback per RFC 5321 §5.1. Reserved TLDs rejected outright.
MX · A · AAAA · IANADisposable match, role patterns, free email provider tag, gibberish score, Levenshtein typo correction, and account blacklist lookup.
Disposable DB · LevenshteinWe enforce eight RFCs in the syntax and DNS layers. Most validators cite one or two. The specs disagree at the edges, which is where incomplete implementations quietly lose addresses.
Defines the transport-level address form that mail servers accept. Length limits, domain label rules, and envelope syntax all live here. This is the spec that decides whether an address can ever be routed.
Plus-addressing. The tag after the plus sign is preserved, not stripped, because it carries routing meaning to the destination mailbox.
.test, .example, .invalid, .localhost are reserved forever. Any address with one of these TLDs is rejected without a DNS query.
Expands reserved-name handling to include .onion, .local, and a few others. These are resolved by special mechanisms, not public DNS, so they cannot hold regular mailboxes.
Defines how DNS names are formed. Each label is 1 to 63 octets, total name up to 255 octets. Labels must not start or end with a hyphen. The validator enforces these at the domain parse step.
Most blog posts cite 320 as the maximum email address length: 64 local + 255 domain + 1 at-sign. That arithmetic is wrong. RFC 5321 §4.5.3.1.3 caps the envelope path at 254 octets. The two extra bytes at 256 are consumed by the < and > in the RCPT TO command. Our validator enforces 254. Addresses beyond it do not round-trip through real MTAs no matter what the naive sum says.
Transparent rule list. Every check traces back to a spec, and when one fails the response tells you exactly why. No hidden magic, no mystery scores.
A handful of TLDs are reserved forever by IETF specs or IANA policy. They cannot resolve to real mailboxes. Our validator rejects them in the syntax layer, before any DNS lookup happens.
Reserved for testing and internal-only use. Never routed on the public internet.
Reserved for documentation and examples. Along with example.com, example.net, example.org.
Reserved to provide a name that will never resolve. Used in negative testing.
Always resolves to the loopback address. Cannot host remote mailboxes.
Multicast DNS (Bonjour) name space. Not part of the public DNS tree.
Tor hidden-service names. Never resolvable via regular DNS.
Reserved by ICANN for private-use DNS. No public delegation.
TLDs must be at least two characters. Single-letter TLDs are never valid.
Gmail, Outlook, and FastMail each interpret local-part characters differently. Our validator processes a canonical field that collapses provider-specific quirks so deduplication catches what string comparison misses.
Edit distance alone is not enough. A naive algorithm thinks kmail and gmail are equally close to gnail. We weight keystroke proximity, so the correction layer always lands on the right domain.
Suggestions come back in the emailSuggested field. Prompt the user or auto-apply. For real-time signup-form validation see the Real-Time API.
The disposable list is an exposed dataset under continuous update. Every entry is flagged with the service it belongs to, first-seen date, and current status. The count below reflects the dataset size at time of writing and grows every day.
Continuously monitored list of burner, temporary, and self-destructing email providers. New services are added to the dataset the moment they surface. Historical entries remain so archived signups still resolve correctly.
Validation is the fastest part of list hygiene. Our bulk email validation service rejects roughly 10 to 15 percent of a typical list before the SMTP verifier layer ever touches them, and up to 20 percent on older, stale lists. Every address that passes moves into SMTP verification cleaner, faster, and without burning credits on obvious junk.
Anyone holding a list of addresses and paying deliverability cost has a reason to validate it. The workflow looks different for each team, but the pipeline is the same.
Run validation before every campaign. Bounce rate stays under two percent, inbox placement stays high, and the ESP keeps seeing a clean sender.
Opt-in outreach lists still accumulate typos, role accounts, and stale addresses over time. Strip malformed, reserved-TLD, and disposable entries before a single send goes out.
Integrate the same pipeline into signup flows via the Real-Time API. Reject typos, disposables, and bots at the door.
Schedule recurring validation against HubSpot, Salesforce, or Klaviyo exports. Mark dead leads, update status fields, keep pipelines honest.
Validate at checkout and in periodic database audits. Order confirmations, shipping updates, and re-engagement campaigns actually land.
Run tens of millions of rows through the Unlimited API. Flat-rate pricing, parallel threads, predictable cost.
"Our previous provider billed credits for validation, so we built a whole pre-upload cleanup step to keep the bill down. Bulk Verify does that layer for free as part of the run. That manual work just disappeared from our pipeline."
"The typo correction response field alone pays for itself. We auto-suggest the corrected domain in the signup flow and recover around four percent of otherwise-bounced users."
"We tested four validators on the same 250k sample. Bulk Email Checker was the only one that correctly flagged the reserved-TLD and disposable addresses the others missed."
Every original column is preserved byte-for-byte in the output. Validation columns are appended alongside, never in place of.
Upload a spreadsheet with any number of custom columns. The validator appends result columns alongside your existing data without touching what was there. No reconciliation work on the way out.
The technical questions that come up most often.
A bulk email validation runs a list of addresses through static checks that do not contact the destination mail server: RFC 5321 envelope syntax, DNS lookups, disposable matching, role patterns, gibberish scoring, and typo correction. It is the first of two layers in our bulk email verification service, catching 10 to 15 percent of bad addresses on typical lists (up to 20 percent on older, stale lists) before the SMTP verifier layer runs.
Validation is the static layer above. Verification is the live SMTP handshake that confirms the recipient mailbox exists via an RCPT TO probe. Validation is cheap and deterministic. Verification is slower and authoritative on mailbox existence. Both layers together give 99.7 percent accuracy. See the bulk email verification for the SMTP half.
Sixteen. They group into three layers: syntax (RFC 5321 envelope, length limits, plus-addressing per RFC 5233), DNS (MX, A, AAAA, RFC 2606 and 6761 reserved TLDs, live IANA feed, RFC 1035 label rules), and intelligence plus cross-reference (disposable database, role patterns, free email provider detection, gibberish, Levenshtein typo correction, blacklist).
The best bulk email validation runs the full pipeline on every address rather than any one check in isolation: RFC 5321 envelope syntax, DNS with MX and A or AAAA fallback, reserved TLD rules per RFC 2606 and RFC 6761, disposable and role patterns, gibberish entropy scoring, Levenshtein typo correction, and provider-specific canonicalization for dedup. Static validation alone is not authoritative on mailbox existence, so a serious tool also pairs validation with live SMTP verification. Bulk Email Checker runs all sixteen static checks plus the SMTP verifier layer in one pipeline at 99.7 percent accuracy.
254. The 320-octet figure most blog posts cite is a miscalculation. RFC 5321 §4.5.3.1.3 caps the envelope path at 254 octets because the angle brackets in the RCPT TO command consume part of the SMTP line length. We enforce 254.
Validation alone catches 10 to 15 percent of bad addresses on typical lists, and up to 20 percent on older, stale lists. Accuracy at the validation layer is deterministic because the checks are either right or wrong against the RFC (a malformed address, a nonexistent TLD, a reserved string, a disposable domain). Validation is not authoritative on mailbox existence, which is what the SMTP verifier layer answers via RCPT TO. Both layers together run at 99.7 percent accuracy across the full pipeline.
RFC 2606 reserves .test, .example, .invalid, and .localhost. RFC 6761 adds .onion and .local. ICANN reserved .internal in 2024. IANA policy forbids single-character TLDs. All are rejected without a DNS query.
Levenshtein edit distance against hundreds of known provider domains, weighted by keyboard adjacency (gnail is closer to gmail than to kmail because g is next to n on a QWERTY layout). TLD swaps like .con→.com are a separate rule. Suggestions return in emailSuggested.
Upload the list as a CSV or TXT file. The validator runs its static checks on every address (RFC 5321 syntax, DNS lookups, disposable database, role patterns, typo correction, gibberish scoring), then the SMTP verifier layer probes every address that survived. Download the enriched list with pass or fail status, intelligence flags, suggested corrections, canonical form for dedup, and all original columns preserved byte-for-byte. Full walkthrough in the How It Works section above.
Free validators typically stop at syntax (the @ check) or a DNS ping, without disposable matching, role patterns, typo correction, or canonical dedup. A real bulk email validation needs every layer on every address. Bulk Email Checker is pay-as-you-go starting at $2.95 for 1,000 validations, with no subscription, no monthly fee, and credits that never expire. The validator layer itself never consumes a credit. Credits are only spent when the SMTP verifier layer runs on what survives validation. For single-address checks, our email checker runs all 16 checks at no cost.
Continuously. The dataset tracks over 272,174 domains and grows every day as new burner services surface. Historical entries remain so archived signups still resolve correctly.
CSV and TXT files. Excel files should be exported as CSV from Excel or Google Sheets before upload. Every original column is preserved byte-for-byte in the output.
Pay-as-you-go starts at $2.95 for 1,000 validations. Volume tiers bring per-address cost down to $0.000132 at 25M. Credits never expire. Unknown results (DNS resolver failures, transient errors) consume zero credits.
Yes. GDPR, CCPA, SOC 2 Type II, ISO 27001, and HIPAA ready. TLS 1.3 in transit, AES-256 at rest, per-tenant isolated containers, configurable retention, and a signed DPA ready for enterprise.
Yes. The same 16 checks are exposed through the Real-Time API with sub-second response times. Ideal for signup forms, checkout pages, and lead capture.
Every quarter at minimum. Lists decay at 2 to 3 percent per month. Always validate before a major campaign and route new leads through the Real-Time API at signup so no bad address ever enters the database.
Email validation is the first and fastest layer of our bulk email verification service. The SMTP verifier runs next on everything that passes. Credits never expire. Ten free validations a day, no credit card.