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. SPF allows email domains to specify which mail hosts are authorized to send emails on their behalf, using the SMTP HELO and MAIL FROM commands. ...