Envelope rewrite by sendmail?

[Chuck Swiger]

On Jan 25, 2017, at 12:42 PM, Trond Endrestøl <Trond.Endrestol at fagskolen.gjovik.no> wrote:
>  A mail messages arrives on the small SMTP server addressed to
>  shorty at short.tld <mailto:shorty at short.tld>. Sendmail, though the aliases mechanism, forwards
>  the message to long.name at some.incredible.long.domain.name.tld <mailto:long.name at some.incredible.long.domain.name.tld>.
> 
>  Antispam measures such as SPF will flag the small SMTP server as not
>  allowed to send email on behalf of the originator.

Yes.  You will need the admins of some.incredible.long.domain.name.tld <mailto:long.name at some.incredible.long.domain.name.tld>
to agree and whitelist your short.tld mailserver if you want it to be a trusted relay.

>  Thus, prior to forwarding each message, the small SMTP server will
>  need to masquerade as the originator and rewrite the envelope's from
>  address to an address within the short.tld domain.

Try not do that, unless both domains belong to you and share a common namespace for
delivery including aliases.  Otherwise, From header munging will break various things,
most commonly mailing lists and bounce handling processing.

Regards,
-- 
-Chuck