Sendgrid Calculates Email Open Rate Differently Than Apollo
Sendgrid counts the number of email opens on a a per-email basis whereas Apollo counts the number of email opens on a per-contact basis.
Contact A = 2 sent emails; both emails were opened
Contact B = 1 sent email; email was not opened
Emails sent = 3 total
In this scenario, Sendgrid will calculate the email open rate as 2 email opens out of 3 total emails sent = 66.67%
Whereas Apollo will calculate the email open rate as 1 contact opened email out of 2 contacts emailed = 50%.