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Welcome, I am Cory. Thank you for asking your question today.
I am sorry to say this, but once you send out an email, it is like mailing it at the post office. You are not able to unsend it after it is sent.
I do apologize for not being able to recall the email you have sent in error.
One thing you can try is to send the same email out with the same subject 20 times in a row. If they have no opened the 1st one, they may just think the account was hacked and delete all of the emails.
I wish I had a better answer for you.
Let me know if you have any other questions.
Please let me know if you have further questions.
If not, please rate my answer with 3 stars or higher and click submit to close the question.