ESP

Email Service Provider - company that you send email through for improved deliverability

• SendGrid (now owned by Twilio)
• ReturnPath
• ExactTarget (now Salesforce Marketing Cloud)
• Mandrill (owned by MailChimp)

You'd like to believe that your ESP's open-rate stats adjust for fake-opens by bot-virus-checkers, but you're probably wrong. In 2020 we discovered that SFMC wasn't doing this, and we had to modify our own stats.

• I can't recall whether we stripped out opens that happened within x seconds of receipt, or by stripping out high-open-volume IP addresses.
• since Apple Mail Privacy features in late 2022, the data is even worse and unfixable