The SPF record is an open standard specifying a technical method to prevent sender address forgery. More precisely, the current version of SPF – protects the envelope sender address, which is used for the delivery of messages.
"v=spf1 +a +mx +include:spf.ax.email ~all"
To authorize additional mail servers, add the server’s IP address before just before the ~all argument of either of the SPF records above, in the format of ip4:address or ip6:address.
Please note: Multiple SPF records are not recommended and may cause delivery and spam classification issues. If you need to authorise more than one mail server for your domain, we recommend that you update your existing SPF record instead of creating multiple records. This SPF record is for our dedicated email hosting. SPF records for shared hosting will differ.
For more information on SPF records, please read more.