new feature: sieve forward plugin

[Brendan Braybrook]

perhaps it would be easiest to add a config option and support to get
dovecot-LDA to use SRS forwarding
(https://en.wikipedia.org/wiki/Sender_Rewriting_Scheme)?

that sorts out the SPF issue and DKIM still works fine (as none of the
DKIM headers are changed). however, you then need to make sure your
mailserver can forward DSNs back to the original sender (as rewriting
the envelope from to your own domain during forwarding causes DSNs to
come back to you from MTAs that are not SRS aware).

On 2022-09-26 03:22, Marc wrote:
> As this page[1] describes a more often occurring problem of forwarding messages from servers that are not included in the spf records. Maybe there should be a plugin that offers this forward functionality. Something like
> 
> get the spf records of the sender
> check if there is a -all
> then apply the sender substitution.
> 
> https://doc.dovecot.org/configuration_manual/sieve/configuring_auto_forward_sender_address/
> 
>