Brand Indicators for Message Identification, part anti-phishing feature, part marketing gimmick. Essentially favicons for email. The Wikipedia article does the

Brand Indicators for Message Identification, part anti-phishing feature, part marketing gimmick. Essentially favicons for email. The Wikipedia article does the best job of summarizing it without marketing industry fluff: https://en.wikipedia.org/wiki/Brand_Indicators_for_Message_Identification https://en.wikipedia.org/wiki/Brand_Indicators_for_Message_I...