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emailemail-headers

Email: legitimate duplicate email header keys with mutually exclusive values

In email the Received: header can legitimately occur more than once with mutually exclusive values...

Received: three.example.com

Received: two.example.com

Received: one.example.com

Are there any other headers can occur in email headers multiple times legitimately?

Solution

  • Ya there are other headers that can appear more than once and is clearly explained here in RFC 5322

    Headers that can appear more than once

    • comments
    • keywords
    • optional-field
    • trace
    • resent-date
    • resent-from
    • resent-sender
    • resent-to
    • resent-cc
    • resent-bcc
    • resent-msg-id

    Check the link above for more clarity.