What are SPF records?

 

When an email enters the system of someone who uses SPF checking (something which is becoming increasingly common) the mail servers look at the SPF record for the sending domain (the bit after the @ in the address) and compare the contents of that record to what they know about the server which sent the mail.  If everything matches then the mail proceeds unhindered but if there is no match or an error then they may either mark the mail with a special flag that tells the mail client to put it in the Junk folder or refuse to deliver it entirely depending on the type of issue.

 

The only solution to this happening is to contact the sender and inform them that their messages are not being delivered properly and that they should ensure their SPF records are set correctly.