歴史

RFC 724

         <extension-field> ::=   "In-Reply-To" ":" <reference-list>
                               |...
         <reference-list>  ::=   <null>
                               | <reference-item>
                               | <reference-item> "," <reference-list>
         <reference-item>  ::=   <phrase>
                               | <mach-host-phrase>
         <mach-host-phrase>::=   "<" <host-phrase> ">"

b. In-Reply-To:

The contents of this field identify previous correspondence which this message answers. If message identifiers are used in this field, they should be enclosed in angle brackets (<>).

例

In-Reply-to: <some string at SHOST>

RFC 733

optional-field =

               ...
            /  "In-Reply-To"":" #(phrase / mach-id)
            /...

2. In-Reply-To

The contents of this field identify previous correspondence which this message answers. Note that if message identifiers are used in this field, they must use the mach-id specification format.

例

In-Reply-To: <some string at SHOST>

RFC 822

     optional-field =
                 ...
                 /  "In-Reply-To"       ":"  *(phrase / msg-id)
                 /...

4.6.2. IN-REPLY-TO

The contents of this field identify previous correspondence which this message answers. Note that if message identifiers are used in this field, they must use the msg-id specification format.

例

In-Reply-To: <some.string@DBM.Group>, George's message

C.3.5. IN-REPLY-TO

The field-body is no longer a comma-separated list, although a sequence is still permitted.

RFC 2822

RFC2822の3.6.4参照。

  obs-in-reply-to =       "In-Reply-To" *WSP ":" *(phrase / msg-id) CRLF

メモ

[1] なんとなく Reply-To 欄との関係を期待したくなるところですが、あんまり関係ないです。 In-Reply-To はそのメッセージが返信する、元メッセージを示し、 Reply-To はそのメッセージを受け取った人が返信する時に使って欲しい宛先が示されます。

歴史