Sender ID, How to Disable a Failed Microsoft Initiative
Sender ID uses 'spf2' to identify the DNS TXT record, leading one to believe that Sender ID is version 2 of the SPF framework. It is not. This misnomer denotes a broken framework championed by Microsoft. Precautions need to be taken to prevent Sender ID from misusing SPF records.
The simplest way to prevent interference with SPF records is to create a Sender ID DNS TXT record with an empty policy as shown below:
Sender ID validation will not misuse the SPF record if the above empty record exists in the domain's TXT field. This effectively turns off Sender ID validation.