In-Reply-To:
Identify previous correspondence RFC2822
The In-Reply-To:
header is used to identify previous correspondence
that the current message is in reply to. This header
is generated by MUAs, not by
sendmail. Prior to RFC2822,
the field for this header was arbitrary text with
one restriction. If that text included the message
identifier, that identifier had to be enclosed in
angle brackets (<
and >
) and had to adhere to the format
for all message identifiers.
Beginning with RFC2822, the In-Reply-To:
header can contain only
message identifiers, each surrounded by angle
braces, and each separated from the next by a
comma.
A typical use of the In-Reply-To:
header might look like the
following:
In-Reply-To: <847.193925.780455@hostA.com>, <1021169802.330@HostB.co.th>,
<200106020731.BAA20313@HostC.br.ca>
↑
whitespace
The In-Reply-To:
header should never be declared in the configuration
file.
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