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 597,191 websites Sender ID Customers. We know of 412,327 live websites using Sender ID and an additional 184,864 sites that used Sender ID historically and 88,626 websites in the United States.
Get a list of 597,191 websites using Sender ID which includes location information, hosting data, contact details, 412,327 currently live websites and an additional 342,860 domains that redirect to sites in this list. 184,864 sites that used this technology previouslyand 88,626 websites in the United States currently using Sender ID.
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