I want to understand the problem.

The problem is very low. I want to figure it out. could you please advise why php mail can send mails automatically? do not all emails require the account and password of the STMP server? mail (to, subject, message, headers, parameters), why is it possible to send it in this way? is it difficult to install each computer? I want to understand it. please advise
Why does php mail automatically send mails? isn't the account and password of the STMP server required for sending mails?
Mail (to, subject, message, headers, parameters). why is it possible? is it a bit confusing if stmp service is installed on every computer?

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Who said no configuration?

[Mail function]
; For Win32 only.
Http://php.net/smtp
SMTP = localhost
Http://php.net/smtp-port
Smtp_port = 25

; For Win32 only.
Http://php.net/sendmail-from
; Sendmail_from = me@example.com

; For Unix only. You may supply arguments as well (default: "sendmail-t-I ").
Http://php.net/sendmail-path
; Sendmail_path =

; Force the addition of the specified parameters to be passed as extra parameters
; To the sendmail binary. These parameters will always replace the value
; The 5th parameter to mail (), even in safe mode.
; Mail. force_extra_parameters =

; Add X-PHP-Originating-Script: that will include uid of the script followed by the filename
Mail. add_x_header = On

; The path to a log file that will log all mail () CILS. Log entries include
; The full path of the script, line number, To address and headers.
; Mail. log =
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You can check php. Configuration in ini
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It indicates that apecha has been configured.
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Yes!
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Discussion

Who said no configuration?

[Mail function]
; For Win32 only.
Http://php.net/smtp
SMTP = localhost
Http://php.net/smtp-port
Smtp_port = 25

; For Win32 only.
Http://php.net/sendmail-from
; Sendmail_fro ......

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This is a good server...
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Cute lz
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If you use sendmail to send emails, you can configure the local machine without smtp.
However, the sending volume is large, and it is easy to be considered as spam rejection.
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Account, password, port, Service mailbox, to be set, nothing else

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You can also set it in the PHP program .. For example, you use QQ to send emails. You can go to QQ mail to enable the SMTP service.