[4] [CITE@en[RFC 976 - UUCP mail interchange format standard]], [TIME[2021-01-24T13:09:17.000Z]], [TIME[2021-03-10T06:35:43.356Z]] <https://tools.ietf.org/html/rfc976>

[37] [CITE@en[RFC 1137 - Mapping between full RFC 822 and RFC 822 with restricted encoding]], [TIME[2021-01-31T11:41:44.000Z]], [TIME[2021-03-13T07:21:00.294Z]] <https://tools.ietf.org/html/rfc1137>