Sender reputation

• Sender reputation is measured by ISPs when E-Mail is received.
• Reputation can be based on sender domains or sending IPs.
• Reputation is built up slowly over time.
• It takes as much time to fix a damaged reputation, as it took to damage it in the first place.

ISP vs. ESP

• An ISP (Internet Service Provider) sends and receives E-Mail on behalf of their customers. Mail from an ISP is commonly expected to be 1:1 and human-to-human communication. ISPs typically provide more than just E-Mail services.
• An ESP (Email Service Provider) mainly sends E-Mail on behalf of its customers. Mail from an ESP is expected to be commercial in nature, optionally comes in large bulks and is machine-to-human communication.