Sender Policy Framework (SPF) is an email validation system designed to prevent email spam by detecting email spoofing, a common vulnerability, by verifying sender IP addresses. SPF allows administrators to specify which hosts are allowed to send mail from a given domain by creating a specific SPF record (or TXT record) in the Domain Name System (DNS).

On our shared platform, SPF records need to consider the range of IP's used during the mail handling process.  Blocking one or any of these could result in your email nt delivering mail.

To cover this range of servers/IP's the following SPF configuration is advised: 

v=spf1 exists:%{i} exists:%{i} -all

This record is applied to the domains DNS as a txt record.

Please raise a support ticket if you need any help with this.