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Re: [ietf-smtp] Is this a valid Message-ID header ?

2020-03-07 19:00:19
On 3/4/20 11:34 PM, John Levine wrote:

I read IETF mailing lists on the IETF's IMAP server* and of late I've been
seeing some awfully funky stuff.

This is an actual Message-ID header in one of the messages in dnsop.
Is that valid?  Even though the MIME decodes to a an ASCII message ID
in the <string@domain> format, I think the answer is no.  That's not
what RFC 5322 sec 3.6 allows.

Message-ID: =?utf-8?q?=3CBN7PR11MB25474DF04998FF3AA9E0B80BC9E40=40BN7PR11MB2?= 

No, it's not valid.   The above field body scans as "atom atom", and a msg-id cannot begin with two atoms without some other symbol (e.g. ".") in between.

RFC 2047 encoded-words were designed to be compatible with the (then-current) RFC 822 grammar, so that they wouldn't break existing parsers.   That means that any decoding of encoded-words for presentation occurs after (header field-specific) parsing. Also, section 5 of RFC 2047 limits use of encoded-words to very specific places in the message header.   Any text that parses as atom that appears elsewhere in a message header, should be treated as an ordinary atom, even if it looks like an encoded-word.


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