Email Syntax Validator

Email Syntax Validator checks lists of email addresses against the practical syntax rules of RFC 5321 and 5322, with optional support for international addresses. It marks every line as valid, invalid, duplicate or empty, explains each error, and lets you copy or download the valid and invalid lists in their original order.

Typos and formatting mistakes in mailing lists cause bounces and wasted sends. Syntax checking catches problems such as missing @ signs, double dots or invalid domains before you import a list. It does not contact mail servers, so it cannot confirm that an inbox exists — that would need a separate verification service.

1. Paste email addresses into the box, one per line.
2. Choose whether duplicates ignore letter case and whether international addresses are allowed.
3. Press Validate.
4. Review the counts and the table; use the Show filter to see one type of result.
5. Copy or download the valid list, the invalid list, or both.

• Bulk checking with one address per line
• Valid, invalid, duplicate and empty-line detection
• A specific reason for every invalid entry
• Case-insensitive duplicate matching (optional)
• Optional international (Unicode) addresses and domains
• Results table with filter and original line numbers
• Copy and Download for valid and invalid lists
• No DNS, MX or SMTP lookups

• Validate lists before importing them into a mailing tool.
• Fix invalid entries at the source where possible rather than only deleting them.
• Use a confirmation (double opt-in) email to prove an address really works.
• Keep the international option off unless your mail system supports it.
• Remember that a valid format does not mean the inbox exists or wants your email.