Email Syntax Checker

The Email Syntax Checker validates each address in your list against standard, RFC-style formatting rules and tells you precisely why any invalid entry fails. Rather than a simple pass or fail, you get a table that marks every address as valid or invalid and, for the ones that fail, spells out the exact problem — a missing @ symbol, consecutive dots, an illegal character, or a malformed domain.

This kind of detailed feedback is far more useful than a plain rejection, because it lets you fix genuine typos instead of throwing good contacts away. Addresses often break in predictable ways: a trailing dot, a double @, a space that crept in during a copy-paste, or a top-level domain that is too short. Seeing the specific reason makes it quick to repair the list and keep contacts you would otherwise lose.

All validation happens locally in your browser using JavaScript, with no upload and no account required. Paste or upload your addresses, run the check, and review the results with a summary of valid versus invalid counts. Because your list never leaves your device, you can confidently validate confidential contact data without any privacy concerns.

Features

• Validates every entry against RFC-style structure rules covering the local part, the @ symbol, and the domain.
• Explains each failure with a specific reason such as missing @, consecutive dots, or an invalid top-level domain.
• Catches common mistakes including double @ symbols, leading or trailing dots, and illegal characters.
• Checks local-part and overall length limits so overlong addresses are correctly rejected.
• Verifies that the domain contains a dot and ends in a plausible alphabetic top-level domain.
• Presents a clear valid-or-invalid table with the reason column filled in for every failure.
• Exports the results to CSV, XLSX, or TXT, or copies them to the clipboard for quick fixes.

How to use Email Syntax Checker

1. Paste your email addresses into the input box, one per line or separated by commas, or upload a file.
2. Click the Check syntax button to validate every entry against the formatting rules.
3. Read the table to see which addresses passed and which failed the validation check.
4. Use the reason column to understand exactly why each invalid address was rejected.
5. Fix the flagged typos in your source list, or remove entries that cannot be repaired.
6. Export or copy the results so you can update your list in a spreadsheet or CRM.

Benefits

• Reduces hard bounces by catching malformed addresses before you import them into a sending platform.
• Saves recoverable contacts by pinpointing typos instead of silently discarding every failed address.
• Speeds up list cleanup because the reason for each failure is shown directly in the results table.
• Protects sender reputation by keeping obviously broken addresses out of live campaigns.
• Works entirely offline in your browser, so confidential lists stay private during validation.
• Gives clear valid and invalid counts so you can measure the overall quality of a new list.

Syntax validation confirms that an address is structurally well formed — it has a sensible local part, exactly one @, and a domain with a plausible top-level domain — but it cannot confirm that the mailbox actually exists or accepts mail. That kind of verification requires live checks against the mail server, which are not possible entirely in the browser. Think of this tool as a fast first filter that removes definite mistakes.

The rules applied here are practical rather than exhaustively RFC-complete, since the full specification permits many rare forms that are almost never used in real lists and would let obvious typos through. The checker deliberately favours catching everyday errors like spaces, double dots, and missing domains. For deduplication and lowercasing after validation, run the results through the Email List Cleaner, and use the Disposable Email Domain Checker to screen for throwaway domains.