SPF

I’ve been trying to receive an email from Instagram, but it wasn’t coming through. Upon inspecting my mail logs, I encountered the following log message: Sep 13 03:50:51 mailserver postfix/smtpd[28105]: NOQUEUE: reject: RCPT from 66-220-155-156.mail-mail.facebook.com[66.220.155.156]: 550 5.7.1 <[email protected]>: Recipient address rejected: Message rejected due to: domain owner discourages use of this host. Please see http://www.openspf.net/Why?s=helo;id=mx-out.facebook.com;ip=66.220.155.156;[email protected]; from=<[email protected]> to=<[email protected]> proto=ESMTP helo=<mx-out.facebook.com> This indicates that the email failed due to SPF (Sender Policy Framework) checks....