forwarding email with sieve of spf domains

[Marc Roos]

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