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SMTP error code · Gmail / Google Workspace

Gmail 550 5.7.1: message is not RFC 5322 compliant

550 5.7.1 Permanent failure (5xx): the message bounced
By iBlockSpam Team Checked against sources 3 sources How we check our content
What it means

Gmail rejected the message because its headers break the Internet Message Format standard, RFC 5322, for example a missing From header, more than one From address or no valid Message-ID.

What the bounce says
550 5.7.1 This message is not RFC 5322 compliant because the From: header is missing. To reduce the amount of spam sent to Gmail, this message has been blocked.

One of several RFC 5322 rejections in Google's SMTP errors reference; others name duplicate headers, multiple From: headers, a non-compliant From: domain or a missing Message-ID.

What 550 5.7.1 means

Google's sender guidelines tell everyone sending to Gmail to format messages according to RFC 5322, the Internet Message Format, and to include a valid Message-ID in every message. Its SMTP reference lists a family of 550 5.7.1 replies for messages that don't: the From: header is missing, there are multiple From: headers or multiple addresses in one, the From: domain isn't compliant, there are duplicate headers, a header is malformed, or the Message-ID is missing or invalid. The text after the code tells you which rule failed.

RFC 5322 section 3.6 says a message needs an origination date and an originator address field, and section 3.6.2 covers From and Sender: if From lists more than one mailbox, a Sender field must name the single sender. Section 3.6.4 says every message should have a Message-ID. Real mail clients get this right; problems come from homemade scripts, website forms, old devices and badly configured relays that build headers by hand.

Because the code is 550, the message bounced and won't be retried. Fix the software that builds the message, send a test to a Gmail address, then resend.

Likely causes

  • A script, form plugin or device builds messages without a From header or a Message-ID.
  • Two From headers, or several addresses in one From header without a Sender header.
  • A From address whose domain isn't valid, such as a bare host name.
  • Duplicated or malformed headers added by a relay, gateway or footer tool.

How to fix it

If you sent the message

  1. Read the exact text after 550 5.7.1: it names the header that failed.
  2. Send through a proper mail library or your provider's SMTP service instead of writing raw headers.
  3. Make sure each message has exactly one From address with a real domain, a Date and a unique Message-ID.
  4. If a relay or gateway rewrites headers, check whether it duplicates any of them.

If you're the recipient or their admin

  1. No action needed at Gmail: the sending system has to produce standard headers.
Email Header Analyzer Email Deliverability Test

Frequently asked questions

Which headers does Gmail require to accept a message?

Google asks senders to follow RFC 5322 and include a valid Message-ID. In practice each message needs a Date, exactly one From address with a valid domain, and a unique Message-ID, without duplicated or malformed headers.

Why does my website form get 'not RFC 5322 compliant' from Gmail?

Form plugins and scripts that build headers themselves often leave out the Message-ID or the From header, or add a second From. Send through an SMTP plugin or mail library that builds standard headers.

Sources

  1. Gmail SMTP errors and codes (Google Workspace Admin Help)
  2. Email sender guidelines (Gmail Help)
  3. RFC 5322: Internet Message Format (section 3.6, field definitions)

Provider messages are quoted as the provider publishes them. Servers can change their wording, so the bounce you received may differ slightly.

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