Recently found I was not getting any emails for a subscribed forum post. I checked our mailserver logs and see this:

Aug 1 16:15:06 tn2 postfix/postscreen[31023]: NOQUEUE: reject: RCPT from [70.169.135.35]:39064: 450 4.3.2 Service currently unavailable; from=<noreply@sawmillcreek.org>, to=<me>, proto=ESMTP, helo=<wsip-70-169-135-35.hr.hr.cox.net>
Aug 1 16:15:58 tn2 postfix/smtpd[31078]: NOQUEUE: reject: RCPT from wsip-70-169-135-35.hr.hr.cox.net[70.169.135.35]: 554 5.7.1 <wsip-70-169-135-35.hr.hr.cox.net>: Unverified Client host rejected: Generic - Please relay via ISP (cox.net); from=<noreply@sawmillcreek.org> to=<me> proto=ESMTP helo=<wsip-70-169-135-35.hr.hr.cox.net>

Is that IP (70.169.135.35) the regular one you send from? So I can whitelist it.