What is SPF and why should I be concerned?
SPF stands for “Sender Policy Framework”. It’s an email authentication technique that is used against email spoofing. An SPF record allows a domain owner to publish a list of the domains or IP addresses that should be trusted to send emails for a given domain.
If a domain or IP that is not on the “trusted list” (so not in the SPF record) attempts to send an email from that domain - it will not pass the SPF security check, indicating that it may be a fraudulent or 'spoof' email. So, criminals can send emails impersonating your domain to your clients, suppliers and other vital business contacts.
How do I resolve this?
To prevent unspecified senders from sending emails on its behalf You should update the "all" mechanism on your SPF record to fix this. Setting this to "-all" will prevent unspecified senders from sending emails on behalf of these domains.