Sender ID is an anti-spoofing email framework heavily based on SPF.
https://en.wikipedia.org/wiki/Sender_ID
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Get access to data on 512,132 websites that are Sender ID Customers. We know of 362,532 live websites using Sender ID and an additional 149,600 sites that used Sender ID historically and 128,148 websites in the United States.
Get a list of 512,132 websites using Sender ID which includes location information, hosting data, contact details, 362,532 currently live websites and an additional 382,118 domains that redirect to sites in this list. 149,600 sites that used this technology previously and 128,148 websites in the United States currently using Sender ID.