Email Syntax Validator
A well-formed address can still bounce
Clu checks the mailbox itself, with an SMTP handshake and catch-all detection, at half a credit per address.
Working a whole list? Upload the CSV to Clu. Get 14 days of Pro, free: 250 credits, 3 seats, agents, Sequences and Clu in Slack.
Start free trialEmail syntax is the set of rules that decides whether an address is well formed. Learn what RFC 5322 allows and which typos to catch, then check the mailbox itself with Clu.
A well-formed address can still bounce
Clu checks the mailbox itself, with an SMTP handshake and catch-all detection, at half a credit per address.
The Free plan is $0 with 50 credits a month and 5 searches. Every new workspace can also try Pro free for 14 days.
- Search
- Free
- Verified work email
- 1 credit
- Phone number
- 10 credits
98% verified work emails and 85% phone numbers on our 500-lead benchmark, across 25+ providers.
A demo of Clu, our agent, doing this for a whole list. Asked: Verify every email in Series B sales leaders before Monday's send. Clu runs the tools, asks for confirmation before spending credits (Validate 480 emails on Series B sales leaders, 240 credits), fills the list row by row and reports: 480 checked: 431 verified, 33 risky, 16 invalid. Want me to drop the invalid ones before Monday?
10,000+ users, from founders to full sales teams
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The Clu Chrome extension finds the verified email and phone number for the LinkedIn profile you have open, in the same tab.
Check email syntax
An email syntax validator checks whether an address is formatted correctly under RFC 5322: a valid local part, one @ symbol, a real domain structure, and a TLD. Watch for common typos like gmial.com too. Syntax is only step one; a well-formed address can still bounce, so verify deliverability before sending.
The toolEmail Syntax ValidatorRunsInside CluFree quotaAccount required
How does this tool work?
Before you send an email, make sure the address is formatted correctly. A valid address has a local part, one @ symbol and a domain with a top-level domain, and it uses only allowed characters. The common failures are missing components, invalid characters and typos like 'gmial.com' or 'outlok.com'. Syntax is a quick first check, because a well-formed address can still bounce.
Clu's email verification checks the mailbox itself with an SMTP check and catch-all detection, at half a credit per email.
Who uses the Email Syntax Validator?
The people who run it most, and what each one runs it for.
- Sales teamsCatch a dead address before a rep spends time writing to it.
- MarketersClean a list before the campaign goes out, so bounces don't hit the sending domain.
- RecruitersConfirm a candidate's contact details are real before you reach out.
- FoundersCheck an address before you email an investor, partner or buyer.
- RevOpsKeep CRM records accurate so routing, scoring and reports hold up.
- AgenciesCheck client data before it goes into a live campaign.
What does Clu do with a whole list?
Watch a real search go from query to an enriched, validated, CRM-ready list: 36 leads, 100% contact fill, synced to HubSpot.
36 ICP leads, 100% contact fill, validated and pushed to HubSpot in one flow
Describe the job once. An agent runs it every week.
Clu turns one sentence into an agent. It searches 1B+ profiles, finds verified emails and phone numbers across 25+ providers, adds the people to your sequence and posts each run to Slack.
Weekly ICP outbound
Built by Clu from: “Every week, find 500 new people who match my ICP, get their emails and phones, and add them to Series B outbound.”
- Searched 1B+ profiles for new ICP matches500 foundPeople Search
- Ran the waterfall across 25+ providers487 emails · 412 phonesWaterfall
- Verified every email and phoneSMTP + catch-allVerification
- Added them to Series B outbound500 peopleSequences
- Posted the run to #pipelineSlackAgents
Friday 4:52 PM15 replies · 5 calls booked
Everything in the 14-day Pro trial
- Clu and agentsDescribe the job in one sentence. Clu builds the agent, runs it on a schedule or a CRM trigger and posts every run to Slack.
- People and Company SearchFind your buyers in 1B+ profiles from one sentence. Searching costs 0 credits.
- Waterfall enrichmentAsk 25+ providers in order and stop at the first verified email or phone number. 98% verified work emails and 85% phone numbers on a 500-lead benchmark.
- Email verificationRun SMTP and catch-all checks on every address before it reaches a sequence, at half a credit an email.
- ICP scoringScore every lead 0 to 100 against your ICP, with the reasons written down. The Research and Qualification skills do the digging.
- SequencesSend email from your reps' own inboxes, with call tasks. A reply stops the sequence. Sending costs 0 credits.
- CRM syncTwo-way sync with HubSpot, Salesforce and Pipedrive. Push finished lists to Outreach, Salesloft and Lemlist.
- Chrome extensionGet a verified email and phone number in one click on LinkedIn, Sales Navigator, Salesforce and HubSpot.
- MCP and APIRun the same search and waterfall from Claude or ChatGPT with 36 MCP tools, or from your own code with the REST API.
14 days of Pro, free: 250 credits, 3 seats, agents, Sequences and Clu in Slack. Then Free at 50 credits a month, or Starter at $49 and Pro at $89 a seat a month.
Which free email lookup tools work together?
Start from whatever you have (a name, a domain, an email or a block of text) and chain the tools until you have a verified contact.
- Email Verifieremailmailbox statusGo beyond syntax: check the mailbox itself with SMTP and catch-all detection. 2 free checks per IP every 30 days.
- MX LookupdomainMX recordsSee the mail servers and SPF setup behind any sending domain.
- Domain ValidatordomainNS, MX, SPF, DMARCConfirm a domain resolves and has valid MX records to receive mail.
- Email ExtractorURL or textevery email on itEnter a website URL or paste text and pull out every email address on it, deduped.
Which paid tool does this for a whole database?
We compared the platforms that do this job for a whole database, Clu included, and say where each one falls short.
- Best data enrichment toolsThe enrichment platforms side by side: coverage, credit costs and what each one verifies.
- Best data enrichment APIsPerson and company enrichment APIs compared on endpoints, coverage, rate limits and price per record.
- Best B2B contact database softwareContact databases compared on accuracy, refresh rate and price once your team uses them every day.
Frequently asked questions
Short answers about the Email Syntax Validator: what it checks, what it costs and where it stops.
All free toolsWhat does email syntax validation check?
RFC 5322 email format compliance: proper use of the @ symbol, valid local part characters, valid domain format, and TLD presence. It's also worth scanning for common typos in popular domains (gmail, outlook, yahoo) and for role-based addresses like info@ or support@.
Is syntax validation the same as email verification?
No. Syntax validation only checks if an email is formatted correctly, it doesn't check if the address actually exists or can receive mail. A syntactically valid email can still bounce. For full verification, use Clu's email verification which checks mailbox existence, catch-all status, and deliverability.
How do I validate emails in bulk?
A spreadsheet can filter out the obvious failures, such as cells with no @ or more than one. For a real check, upload a CSV to Clu, which checks each mailbox with an SMTP check and catch-all detection at half a credit per email.
Now run it on the whole list.
Upload the CSV or describe the list you want. Clu finds, verifies and qualifies every row.
14 days of Pro, free.