Hi, my name is ***** ***** welcome to JustAnswer!
I'm afraid that once an e-mail has been sent, it leaves your account and is routed to a completely different network and set of servers and the e-mail cannot be retrieved. It is at that point physically in the hands of the recipient, so to speak.
There IS an "undo Send" feature in Gmail, but this has to be turned on in advance and it only works for 30 seconds. After 30 seconds, even with the feature enabled, the e-mail cannot be pulled back.
I really wish I had a better answer for you and I'm sure this is frustrating. If you have any other questions on this, just let me know and I'll help you in any way that I can.
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