Windows xampp で smtp4dev を使っています。

php.ini の設定

[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 = "\"C:\pleiades\2022-09\xampp\sendmail\sendmail.exe\" -t -i"

sendmail.iniの設定

[sendmail]

; you must change mail.mydomain.com to your smtp server,
; or to IIS's "pickup" directory.  (generally C:\Inetpub\mailroot\Pickup)
; emails delivered via IIS's pickup directory cause sendmail to
; run quicker, but you won't get error messages back to the calling
; application.

;smtp_server=mail.mydomain.com
smtp_server=localhost

; smtp port (normally 25)

smtp_port=25

; SMTPS (SSL) support
;   auto = use SSL for port 465, otherwise try to use TLS
;   ssl  = alway use SSL
;   tls  = always use TLS
;   none = never try to use SSL

smtp_ssl=auto