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Old 30 Jan 2019, 01:25 AM   #5
BritTim
The "e" in e-mail
 
Join Date: May 2003
Location: mostly in Thailand
Posts: 3,084
Quote:
Originally Posted by JeremyNicoll View Post
Wouldn't a rule for:

A header called In-Reply-To: does not exist

help?
I had forgotten the In-Reply-To (and References) headers. Indeed, while technically optional, almost all mail clients these days will add an In-Reply-To header as recommended in the RFC (see https://tools.ietf.org/html/rfc5322 Section 3.6.4).
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