When parsing a collection of MBox files, I came across a surprising number of Date header fields of the form:
"Date:" date-time "<" addr-spec ">"
Reading the available RFCs I find no matching syntax. The valid form appears to be:
"Date:" date-time [CFWS]
CFWS represents comments plus folding whitespace as described in Section 3.3 (Date and Time Specification) of RFC5322.
Reading Proper Mail Date Header Formatting where the author analyses 132k date headers, yet the form above never shows in the linked dataset.
Is this an MBox artefact, IMF attribute, or corruption from a mail agent and/or mail relay?
The Internet Message Format has been evolving since the 1980s, it's a bit of a mess and has been interpreted a number of ways à la HTTP. I'm leaning toward this being a vendor-specific modification that results in a malformed Date header field? IDK.
Example MBox
From ???@???
From: from@mail.com
To: to@mail.com
Date: Sat, 02 Feb 2002 00:55:01 +0000 <name@mail.com>
Subject: Email One
This is email 1.
Specifications
