CODEWITHSUNDEEP
emailmimeemail-headers
zby
zby

Reputation: 2465

What email header fields can have parameters?

I am trying to find out what universal subroutines can I have in an email parsing library.

I know of two MIME fields that often take parameters:

Content-Type: application/x-stuff;
 title*=us-ascii'en-us'This%20is%20%2A%2A%2Afun%2A%2A%2A

(example from https://www.rfc-editor.org/rfc/rfc2231)

and

Content-Disposition: attachment; filename=genome.jpeg;
 modification-date="Wed, 12 Feb 1997 16:29:51 -0500";

(example from https://www.rfc-editor.org/rfc/rfc2183)

Are they the only ones - or is this an universal mechanism? https://www.rfc-editor.org/rfc/rfc822 only talks about 'structured' fields - the fields above are 'structured' for sure, but the example in rfc822 is about an address field - which is a different structure - list of addresses.

Upvotes: 0

Views: 809

Answers (2)

tripleee
tripleee

Reputation: 189628

The Received: header is typically structured, although the spec is rather vague and there is no serious standardization effort. The closest thing resembling a de facto standard is Sendmail, which is mimicked more or less closely by Postfix. The DKIM signature is structured, in a fairly clever way. The ad hoc header inserted by SpamAssassin has a structure; it tells you why a message was classified as spam. There are oodles more, but this should give you something to start chewing. None of the examples here use the Mime Content-xxx syntax.

Upvotes: 1

Moritz Both
Moritz Both

Reputation: 1628

There are two more MIME fields in email as far as I know:

MIME-Version: 1.0

which has no parameters, and

Content-Transfer-Encoding: ...

has none, either.

There is no general "MIME header field parameter rule", just look up the standard definition for each header field.

(EDIT:) After your additions to the original question, you can of course use universal subroutines. Be warned that email heaader parsing is a nontrivial task (cf. RFC 2822). These universal subroutines come into my mind:

  • Remove comments in the header fields (denoted by parenthesis).
  • Handle tab indent lines (continuation lines)
  • Parse RFC822 date/times (huge task :)
  • Handle quotation
  • Parse email addresses (different forms)
  • Handle character encoding (MIME header encoding)

However, all this exists in many open source libraries of course.

Upvotes: 1

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