Bulk email domain DKIM checker: does each address's domain publish a DKIM key?
In short: Paste email addresses and see whether each domain publishes a DKIM key at the 22 common selectors, with the selector and key length in the CSV. Limit: Reads the domain, never the mailbox: a DKIM key says nothing about a particular address.
A bulk email domain DKIM checker reads the domain after the @ in each address and looks up DKIM keys at 22 common selector names in DNS. Paste up to 100 unique domains a run, or 500 signed in. Each row shows the key found, a weak or broken key, or no key at the common selectors. It checks the domain, not the mailbox. Download the CSV.
A DKIM key doesn't make the mailbox real. Check every address.
Price: this tool is free. Checking a whole email list is from $9/mo, and the first 100 checks are free with Google, no card. Check your list free nowSee pricing
Sample result
tom@globex.example is at a domain that publishes a 2048-bit DKIM key at selector1.
- Address
- tom@globex.example
- Selector
- selector1
- Key length
- 2048 bits
What this means for you
A key shows the domain signs mail. It says nothing about whether the mailbox exists.
- Key length and problems flagged
- Weak, revoked and broken keys
- Private selectors not found, said plainly
- CSV out, nothing emailed
- DKIM
- Selectors
- CSV
By SimpleVerifier Team · Last updated
Got a list of company addresses and want to see which domains sign their mail?
- Paste it above to look up each domain's DKIM keys at the common selectors, with the selector and key length in the CSV.
- Upload or paste it at /verify. Every address gets a live mailbox check, and the first 100 email checks are free with a Google sign-in, no card.
How do I check DKIM for the domains on an email list?
- Paste email addresses, one per line, or upload a CSV. Addresses are found anywhere in the text, so a whole export works.
- Press Check DKIM. Only the unique domains are sent, never the mailbox names, 10 a request: DNS queries at common selector names, nothing sent to the domains and nothing stored. No mail is sent.
- Read each row: Key found, Weak key, Testing, Revoked, Broken, CNAME to nothing, or No key at common selectors.
- Download the CSV with the selectors that had keys and the key length beside each address, and hand the list to the mailbox check.
Example
- You enter
- Four addresses:
jane@acme.example(a 2048-bit key at selector1),tom@globex.example(a 512-bit key),ana@initech.example(a CNAME at a selector pointing at nothing) andbo@umbrella.example(no key at any common selector). - You get
- jane: Key found. tom: Weak key. ana: CNAME to nothing. bo: No key at common selectors. The selectors and key lengths are in the CSV.
- Limits
- Up to 100 unique domains a run without an account and 500 when signed in with Google. 10 domains a request; DNS only, 22 common selectors. A private selector is not found.
What does the check read?
A TXT and a CNAME query at selector._domainkey.domain for each of 22 common selector names (such as google, selector1, selector2 and default), plus one wildcard probe, all in DNS. A key found is read for its type and length, and flagged when it is revoked, in testing mode, shorter than 1024 bits or broken. DKIM is defined in RFC 6376.
A domain can sign with a selector name that is not on the list, so No key at common selectors does not prove it signs nothing.
Why check DKIM on an email list?
A domain with a DKIM key is set up to sign mail, which is a sign someone configured email for it. The check is most useful for sorting a list of company domains by how they send, not for deciding whether an address works. A list of thousands of addresses has far fewer unique domains, so querying one set of selectors per domain is cheap.
Free mail domains such as gmail.com are looked up like any other domain, and often publish no key at these selectors.
What do you do with the rows?
Keep the CSV as a record of how each domain sends. To read SPF and DMARC for the same list, use the bulk email SPF and DMARC checker, and to see who runs each domain's mail, the bulk email provider lookup.
Before you email anyone on the list, verify the addresses.
Who uses this tool, and for what?
- Sales teams
- Sort a lead list by whether each company's domain signs its mail.
- Deliverability teams
- Spot weak, revoked or broken keys among the domains you mail.
- Agencies
- Find client-list domains with no DKIM set up.
- Developers
- Triage a signup export for domains with a broken key record.
What can’t this tool tell you?
- Reads the domain, never the mailbox: a DKIM key says nothing about a particular address.
- Only 22 common selector names and one wildcard probe are tried, in DNS. A private selector is not found.
- A key found is read for type and length; whether the domain's mail passes DKIM depends on what it actually sends.
- Up to 100 unique domains a run without an account, 500 signed in. Free providers such as gmail.com are looked up like any domain.
Common questions
- How do I check DKIM for the domains on an email list?
- Paste the list into a bulk email domain DKIM checker like this one. It reads each address's domain and looks up DKIM keys at 22 common selectors in DNS.
- Is this bulk email domain DKIM checker free?
- Yes. It is a free tool: up to 100 unique domains a run with no account, and up to 500 a run when you sign in with Google, with no card.
- Does a DKIM key mean the mailbox exists?
- No. It checks the domain, not the mailbox. A key shows the domain signs mail, not that an address is real.
- Why does a row say No key at common selectors?
- None of the 22 common names published a key. A domain can use a private selector, so that is not proof it signs nothing.
- Can I check my own selector?
- Not here. Use the bulk DKIM checker on the domains, which takes up to three selectors you type.
- Does it send an email to the domain?
- No. It sends DNS queries only and never connects to a mail server.
Sources
A tidy list can still be full of dead addresses.
Extracting, deduplicating and syntax checks all work on the text of an address. None of them can tell whether the mailbox exists. Only the server that hosts it can answer that, through an SMTP check, and that is what the paid product does.
- Upload the cleaned file as it is: CSVs up to 100,000 rows
- A real SMTP mailbox check on every row, with catch-all detection
- Small list? Starter at $9/mo covers 2,500 emails a month, cancel anytime
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.