Sender ID is an anti-spoofing email framework heavily based on SPF.
https://en.wikipedia.org/wiki/Sender_ID
Email Hosting Providers
Get access to data on 671,300 websites that are Sender ID Customers. We know of 472,010 live websites using Sender ID and an additional 199,290 sites that used Sender ID historically and 102,135 websites in the United States.
Get a list of 671,300 websites using Sender ID which includes location information, hosting data, contact details, 472,010 currently live websites and an additional 367,279 domains that redirect to sites in this list. 199,290 sites that used this technology previouslyand 102,135 websites in the United States currently using Sender ID.
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