who opened SES email?

Hello Adam.

Unless there is some context I'm not finding from what you describe, I'd say If you send an email to a specific address, and then get a notification that the email was opened, then it means that the email was delivered to the intended mailbox for the email address which consequently would indicate that the owner of the email address is the one that opened the email.

I hope this helps.

Hello Adam, Considering that you have used AWS SES notification service using configuration set, I recommend to send emails on a one to one basis to find who actually opened or clicked the message. In SES, all notification event types are not unique to the recipient while sending an email through SES for multiple recipients, with the exception of Bounce & Complaint notification types. For this reason, I recommend that you send emails on a one to one basis, that is one email per recipient.

https://docs.aws.amazon.com/ses/latest/dg/monitor-sending-using-event-publishing-setup.html