CODEWITHSUNDEEP
emailemail-headers
romanofski
romanofski

Reputation: 1132

What do X-headers in mails stand for?

I'm wondering what all X- headers in e-mails stand for.

Thank you for shedding some light in that field :)

Upvotes: 12

Views: 15296

Answers (1)

user149341
user149341

Reputation:

RFC822 ("Standard for the Format of ARPA Internet Text Messages") specified in sections 4.7.4 and 4.7.5 that headers beginning with "X-" would not ever be part of any standard, and thus can be used for application-specific purposes.

For what it's worth, the more recent BCP document RFC6648 ("Deprecating the 'X-' Prefix and Similar Constructs in Application Protocols") recommends that the use of the "X-" prefix be avoided in the future, as the distinction between standardized and nonstandardized headers is not well defined, and attempting to draw such a distinction fails when commonly used nonstandard headers are adopted as standards.

Upvotes: 21

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