A consumer ISP wants their users to be happy using their service, including seeing mail they want to receive, and not seeing mail they didn't want. An enterprise mailbox provider wants the corporation paying for the service to be happy, and amongst other things that means that they want their users to be able to do their job efficiently, to have no problems receiving work-related email and not to be distracted by other email.
Engagement data include whether a user has opened an email, deleted it, replied to it, or moved it to another folder. Providers with webmail or mobile clients can also track clicks, scrolling, time spent, and more.
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