以下內容是參考 https://kifarunix.com/configure-postfix-to-use-gmail-smtp-on-ubuntu-18-04/
首先安裝一下 postfix 與 mailutils
$ sudo apt install postfix mailutils
安裝過程設定使用 Internet site: Mail is sent and received directly using SMTP.
安裝後修改 /etc/postfix/main.cf
relayhost = [smtp.gmail.com]:587 smtp_sasl_auth_enable = yes smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd smtp_sasl_security_options = noanonymous smtp_tls_security_level = encrypt smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
修改 /etc/postfix/sasl_passwd 加入密碼
[smtp.gmail.com]:587 userid@gmail.com:password
應用程式密碼可以在 https://myaccount.google.com/apppasswords 產生
使用 postmap 產生 db
$ sudo postmap /etc/postfix/sasl_passwd $ ls /etc/postfix/sasl_passwd* /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
變更 /etc/postfix/sasl_passwd* 權限
$ sudo chown root:root /etc/postfix/sasl_passwd* $ sudo chmod 600 /etc/postfix/sasl_passwd*
設定完成後重啟 postfix
$ service postfix reload
最後寫一封信寄給自己看看有沒有成功收到
$ echo "This is a test mail." | mail -s "test mail" userid@gmail.com
