Comment 9 for bug 1857618

https://marc.info/?l=postfix-users&m=157746682807997&q=mbox

>> 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