How to obtain the current email address in the email system

In the mail system, how do I obtain the current email address? I want to subscribe to and unsubscribe to the email address of the recipient in other people's emails? But how can this be obtained? How to obtain the current email address in the email system
If I want to subscribe to and unsubscribe, what is the recipient's email address in someone else's email?
But how can this be obtained? Share:
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Each person should have a corresponding email address. can you find another email address based on the person?
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So what is the recipient's email address in others' emails?

What does this mean? The user subscribes to a natural input email or the email address of the currently logged-on user. of course, the database is saved,
I don't know what you're talking about?
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I understand what you mean ..
First, generally, if you subscribe to or unsubscribe to, link is provided in the email and then direct to a webpage. for example, if you receive an advertisement email from Amazon, generally, there is a "unsubscribe" link at the bottom of the mail body. click the link browser to open a new webpage where you choose to unsubscribe. why do you want to reply to the email to unsubscribe?
If you must reply to the system Email, php's mail function generally has the following parameters:
Mail ($ to, $ subject, $ message, $ headers)
To is the recipient's address, $ subject is the Mail subject, $ message is the mail body, and $ headers, you can set the sender's mailbox in it, this is what you call the "recipient's email address in others' emails"
For example, I write:
$ Headers = "From: system_admin@hotmail.com"
Mail ($ to, $ subject, $ message, $ headers)
Then your recipient will receive an email, and the sender shown in the email is "system_admin@hotmail.com"
If she replies to this email, "system_admin@hotmail.com" will receive

I wonder if you want to ask?