in our theatre we use Zimbra as the official mail server.
for mail about ticketing we use the mail servers of a third party, the ticketing supplier. they send mail about tickets on our behalve.
sometimes it happens clients does not recieve their ticket mail because of discrepancies in mail headers between our mail-domain and the third party mail-domain.
from our server we use a spf header for our own domain. the third party uses a spf header as well for their domain.
to avoid clients not receiving mail from ticketing the supplier suggests to add a spf file for the ticketing domain on our mail server.

some of the questions rising are:
1. isn't this just a dns matter
2. shouldn't it be the other way around: our spf file installed on the mailserver at the ticketing supplier.
3. is there a need to install extra spf files on our server
4. at last: if so, how to

does anyone have any experience on this matter which can lead me to a solution? looking forward to hear from someone, regards