Frequently Asked Question
RFC5322 requirement error means the message is not structurally valid for us to inspect it safely. In most cases postfix and it's filters cannot parse the message headers as a compliant RFC 5322 email, so evaluation stops before DMARC/SPF/DKIM alignment is fully considered and content filters are engaged.
In practical terms, this is a message format problem, not a DNS problem. We rarely see this because most modern email gateways enforce basic compliance with the standards so refuse to originate malformed email, but it should be noted that scammers/phishers do deliberately malform headers in an attempt to bypass some weaker mail filters by confusing them.
We CANNOT white-list or in any way permit these messages to proceed - they are malformed and it would be unsafe.
What the error usually means
DMARC relies on the visible message headers, especially the From: header defined by RFC 5322. If that header is missing, duplicated, malformed, or the message headers are otherwise broken, OpenDMARC will report an RFC 5322 requirement error.
Most likely causes
Missing From: header
message processing requires a valid visible author address.
If From: is absent, filters cannot determine the domain to evaluate.
Malformed From: header
Common examples include:
missing @
invalid characters
broken quoting
unbalanced angle brackets
incomplete address formats
Multiple From: headers
RFC 5322 allows only one From: header field.
More than one makes the message invalid for filter purposes.
Corrupt or badly formed message headers
Headers may be truncated, concatenated incorrectly, or rewritten into an unparsable form by an application, script, relay, or gateway.
Missing Date header or multiple Date headers
RFC822 mandates one and only one valid Date header in the standard defined format, e.g.
Date: Wed, 01 Jan 2026 10:20:30 +0100
Missing blank line between headers and body
A valid message must have a header section, then a blank line, then the body.
Without that separator, parsers may treat the message as malformed.
Invalid header folding
Long headers may be folded across lines, but continuation lines must begin with whitespace.
Incorrect folding can make a header unreadable.
Bad line endings
SMTP messages should use standard CRLF line endings.
Some poorly written software generates non-standard line endings or mixed formatting.
Non-ASCII or badly encoded header content
Header values containing non-ASCII text must be encoded correctly.
Broken MIME or encoded-word formatting can cause header parsing failures.
Truncated message data
If the message is cut off during submission, relay, or storage, required headers may be incomplete.
Message rewriting by a gateway, filter, scanner, copier, or application
Devices and software that alter headers can accidentally create duplicate fields, invalid folding, or broken address syntax.
Invalid sender-style fields generated by custom software
Applications that build raw email manually sometimes create syntactically invalid headers that stricter parsers reject.
Most common real-world sources of the problem
- website contact forms using poor mail code
- PHP or custom scripts building raw mail headers manually
- multifunction printers and scanners sending email directly
- monitoring systems and appliances with basic SMTP implementations
- security gateways or mailing systems that rewrite
From:badly - third-party software that injects duplicate headers
