What are common RFC compliance issues that break deliverability?

Common RFC compliance issues include malformed headers violating RFC 5322 (incorrect date formats, missing required fields, improper line folding), which can trigger spam filters or cause display problems.

SMTP violations like improper HELO/EHLO identification, missing reverse DNS, or ignoring bounce handling requirements cause delivery failures and reputation damage. Authentication misconfigurations violating SPF, DKIM, or DMARC RFCs trigger authentication failures.

Content encoding errors violating MIME specifications cause display issues or trigger filters suspicious of malformed messages. Line length violations, improper character encoding, and boundary errors create problems across email clients. Rigorous RFC compliance prevents these deliverability issues.