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Email Syntax Checker

Validate email address format against RFC 5322 standards and flag formatting errors.

Category
Email Validation & Verification
Type
Checker
Price
Free, no signup

Email Syntax Checker

Check Email Syntax

Enter an email address to validate its syntax against RFC standards.

Testing this tool with an AI agent
  • Open this page in a browser. Email Syntax Checker is the form at the top of the page.
  • Fill every field with sample values. Use made-up data, never real customer data.
  • Press the main button and wait for the result to show on the page.
  • No login, API key or install is needed.

What it does

  • RFC compliance check
  • Error highlighting
  • Correction suggestions
  • Bulk checking
  • Detailed explanations

When to use it

  • Data validation
  • Form checking
  • List cleaning
  • Quality assurance

About Email Syntax Checker

The Email Syntax Checker validates email address format according to RFC standards. Identify formatting errors, invalid characters, and structural issues in email addresses.

Frequently asked questions

How does Email Syntax Checker work?

Fill in the form at the top of this page and run it. The result shows on the same page. No account or install needed.

Is Email Syntax Checker free?

Yes. It is free and needs no signup. Use it as often as you like.

How much should I trust the result?

Use it as a quick check. It follows common email validation & verification rules, so check anything important again before you change live settings.

Can I use it for work?

Yes. You can use it for personal and work tasks.

Should I paste private data into it?

No. Like any online tool, never paste passwords, API keys or private customer data.

Outreach that keeps going after you log off.Leads, emails, follow-ups and replies, handled.

Connect unlimited mailboxes and let AI agents find leads, write each email and follow up. Or send your own templates in manual mode. From $29/mo.

Start your $1 trial See pricing

$1 for 3 days · Cancel anytime · No contract

Install with AI

Your coding agent sets up the FirstSales CLI and skills for you.

Prompt for Claude Code

I'm setting up FirstSales (https://firstsales.io), an AI outbound sales platform: campaigns, contacts, a reply inbox, deliverability and lead signals. Help me get my workspace sending real, good emails end to end, from Claude Code.

Read these first so you know how FirstSales works:
- Developer docs and API: https://developer.firstsales.io
- CLI: https://www.npmjs.com/package/@firstsales.io/cli
- Skills for coding agents: https://github.com/firstsalesio/firstsales-skills (read README.md and GUIDE.md)

Setup
1. Install the CLI: npm install -g @firstsales.io/cli
2. Install the FirstSales skills:
   claude plugin marketplace add firstsalesio/firstsales-skills
   claude plugin install firstsales@firstsales
3. Ask me if I already have a FirstSales account. If not, send me to https://app.firstsales.io to sign up.
4. Ask me to create an API key under Settings → API → API Keys, with only the scopes we need.
   Never ask me to paste the key into this chat. Tell me to run this in my own terminal, so the key stays hidden:
   read -rs FS_KEY && firstsales auth login --api-key "$FS_KEY"; unset FS_KEY
5. Run `firstsales whoami` and tell me which workspace and organisation we are connected to.

Then ask me about my business: what I sell, who I sell to (roles, company size, countries), my best customers, and what I use today for outbound (tools, lists, mailboxes). Walk me through:
1. Teaching FirstSales my business: website, offer, proof points and case studies in the knowledge base, so the AI writes like someone who knows the product.
2. Connecting my sending mailboxes and checking my sending domain: SPF, DKIM, DMARC and warm-up. If anything is unhealthy, tell me the exact DNS record to add.
3. Bringing in contacts: import my CSV or CRM export into a clean list, remove duplicates and bad emails, and block domains I must never email (customers, competitors, my own).
4. Building my first campaign: the right list, senders, steps and timing. Write the sequence with me, show me the drafts, and do not launch until I say yes.
5. Setting up Signals if it fits: find people engaging with LinkedIn posts about topics my buyers care about, and turn them into leads.
6. Inviting my team and giving each person the right access.

Once campaigns run, show me how to work the reply inbox from here: which replies need an answer, draft responses in my voice, and move good conversations into deals. If I use Cal.com, connect it so follow-ups can offer my booking link (not the first email).

Throughout, as you learn about my business, proactively suggest and help create:
- Reply templates for the questions and objections my prospects are likely to raise, based on my product, site and codebase if you can see them.
- Campaign ideas and segments worth testing, with the reason for each.

Safety rules:
- Show every change as a dry run (--dry-run) first and wait for my yes. Never send emails, launch campaigns or delete anything without my yes.
- Tell me before anything that spends credits, and how many.

Be opinionated. If the docs give a sensible default, just use it. Don't make me choose between five options.
Developer docs ↗npm: @firstsales.io/cli ↗GitHub: firstsales-skills ↗