msd+postfix-us...@msd.im:
> Hi all,
>
> With `milter_protocol = 2`, the DKIM signature is invalid if a signed
> header is like "Subject:" in this test.eml attached example.
>
> ```
> From: <t...@example.com>
> To: <t...@example.com>
> Subject:
>
> Folding_White_Space_and_too_long_subject_aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
>
> Test
> ```
>
> It works fine with `milter_protocol = 6`.
Which is the default value.
Milter protocols versions < 6 don't support the SMFIP_HDR_LEADSPC
feature. This feature was introduced with Sendmail 8.14, and is
needed to correctly preserve the leading whitespace of a header
field value.
Wietse
Sendmail 8.14.0 RELEASE_NOTES:
LIBMILTER: A milter can receive header field values with all
leading spaces by requesting the SMFIP_HDR_LEADSPC
protocol action. Also, if the flag is set then the MTA
does not add a leading space to headers that are added,
inserted, or replaced.
sendmail-8.14.0/libmilter/docs/xxfi_header.html:
Starting with sendmail 8.14, spaces after the colon in a header
field are preserved if requested using the flag SMFIP_HDR_LEADSPC.
That is, the header
From: sender <f...@example.com>
To: user <t...@example.com>
Subject:no
will be sent to a milter as
"From", " sender <f...@example.com>"
"To", " user <t...@example.com>"
"Subject", "no"
while previously (or without the flag SMFIP_HDR_LEADSPC) it was:
"From", "sender <f...@example.com>"
"To", "user <t...@example.com>"
"Subject", "no"
In the implementation, Sendmail skips only the first space character
before a header value, so the documentation and code disagree.
Postfix implements Sendmail behavior.
