On Sunday, 25/10/2020 at 11:48 Marc Roos wrote:

Say someone has setup spf for his domain and sends an email to a user
that has in roundcube enabled the sieve forward. If the message is
forwarded without altering the message headers, this could result in a
message being blocked or not relayed, because sending hosts ip, is not
in the spf of the from: domain.

Possible solutions are:

-  add option if enabled, it replaces the From: with that of the email
address of the sieve user. (Maybe move the original sender to the
Reply-To header? Maybe exception for 'internal' forward?)
-  Upon processing the message, check the spf records, if they are
enforced, do the above, otherwise do nothing.


https://tools.ietf.org/html/rfc5228#section-4.2