Hi You've implemented SPF within Postfix which is fine.
Ik think the email of the sender can not pass as it seems that their domain DNS-settings does not contain a SPF-record.
If they define a SPF-record, i do think email will pass through.
So this is the best option.
The other possibility is that you remove the line:
rivate/policy from your Postfix configuration file and restart Postfix afterwards.
In that case your system does not check for SPF-records anymore, but i don't recommend that.