> On Sep 26, 2017, at 11:23 PM, Michael Fox <n...@mefox.org> wrote:
>
> BTW, the mail provider found that the default sendmail config and their own
> customized config both rewrote the From: header when the From: address was
> for a domain that had a CNAME record. They said this is a config option in
> sendmail and they prefer to operate this way. Interesting that my other
> Postfix machines don't do this, nor do many other large email providers.
This is an obsolete option in Sendmail that violates decades old SMTP
standards, CNAME canonicalization of recipient domains went away in
RFC 2821 and there are many email domains that are aliases where the
mailbox address is expected to remain unmangled by CNAME expansion of
the domain part. The operators of the sending system are stuck in the
distant past.
--
Viktor.
