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Email error 553 5.1.3: Invalid address syntax

The recipient address is not written in a valid format, so the server refuses it before looking for a mailbox.

Permanent failure (hard bounce)

What it means

The recipient address is not written in a valid format, so the server refuses it before looking for a mailbox.

Common causes

  • A missing or doubled @ sign.
  • Spaces, commas or other illegal characters in the address.
  • A missing domain part or a domain with a typo in the ending.
  • Data imported with extra characters, such as quotes or line breaks.

How to fix it

  1. Open the address in a text editor and remove spaces and stray characters.
  2. Fix obvious typos such as .con instead of .com.
  3. Clean the column in your spreadsheet before you export it.
  4. Validate the format at sign-up so bad addresses never enter the list.

How to prevent it

Remove the address from your list and verify the rest before the next campaign.

Most bounces come from addresses that were never checked. Verify each address before you send: syntax, domain, mailbox and risk are checked without sending a message. Test a single address with the free email checker or upload a whole list for bulk verification.

Verify an email address free · Clean a whole list · MX lookup · SPF, DKIM and DMARC checker

Frequently asked questions

Can a syntax error be fixed automatically?

Sometimes. Trimming spaces and fixing common domain typos solves many cases, but always review the changes.

Does syntax validation prove the mailbox exists?

No. It only proves the format is legal. A full check also looks at the domain and the mailbox.

Other error codes

550 5.1.1User unknown (mailbox does not exist) 550 5.7.1Message rejected by policy (blocked) 550 5.7.26Sender not authenticated (SPF/DKIM/DMARC) 550 5.4.1Recipient address rejected: access denied 552 5.2.2Mailbox full (over quota) 554 5.7.1Transaction failed: service unavailable or blocked

All email error codes