Are RFCs optional?

Technically, RFCs are voluntary standards that software implementations can choose to follow. In practice, significant deviation from RFCs causes interoperability problems that make email systems non functional.

An email server that does not implement RFC 5321 SMTP cannot communicate with other servers. Authentication that deviates from DKIM or SPF RFCs will not validate. Practical necessity makes RFCs effectively mandatory.

Some RFC provisions are more optional than others. Recommendations and best practices within RFCs may be ignored with fewer consequences than core protocol requirements. Understanding which provisions are critical versus advisory helps prioritize compliance.

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