This means that the SPF (Sender Policy Framework) has been broken. If this is legitimate mail, then this could be due to a forwarding construction. Please see our SPF knowledge base article below for more information.
SPF (Sender Policy Framework) is a way to restrict which mail servers are allowed to send email for your domain name.
An example of an SPF would be :
example.com. TXT "v=spf1 -all"
SPF records are TXT records placed into a domain's DNS settings. To setup a SPF record we recommend using the following link.
Be advised that forwarding emails can sometimes break the SPF. If this is the case we recommend using SRS (Sender Rewriting Scheme). More information about this can be found here.