How do I whitelist a domain in Postfix?

[FatalError]

I saw one how-to covering this, but it didn't look the same as my SpamSnake setup. Anyway here is my issue:

One of our vendors is being rejected on an SPF check.

Someone told me that they had very recently changed ISPs.

Here's a log entry from Postfix:

Sep 10 15:25:21 spamsnake postfix/smtpd[24756]: NOQUEUE: reject: RCPT from unknown[their.ip.addr.here]: 450 4.7.1 <myuser@mydomain.com>: Recipient address rejected: SPF-Result=mail.theirmailserversdomainname.com: 'SERVFAIL' error on DNS 'SPF' lookup of 'mail.theirmailserversdomainname.com'; from=<theiruser@theirdomain.com> to=<myuser@mydomain.com> proto=ESMTP helo=<mail.THEIRMAILSERVERSDOMAINNAME.COM>

Maybe they haven't updated their SPF record after the ISP change?

Anyway, is there a way to whitelist their domain(s) in Postfix so my users can receive mail from them?


UPDATE: after checking a few online dns query sites, I have determined that there is NO SPF record for either of their domain names. This doesn't sound right...

If anyone wants a crack at this, their email server's name is mail.cbsinsne.com and their email address domain is fainsgroup.com.