MAC
1. Start the Mail program.
2. Open the “Preferences” window. Click Mail, then Preferences:
The preferences window will appear.
3. Choose the “Account Information” screen.
Navigate to the “Account Information” screen. To do this:
- Click Accounts (the blue “@” sign) along the top of the window if necessary.
- Click the address@example.com account in the left “Accounts” column if necessary.
- Click Account Information if necessary.
4. Disable "Remove copy from server".
Uncheck "Remove copy from server after retrieving message".
(The “Description” section doesn’t matter and may say something else, although it’s easier to keep track of multiple addresses if you set it to be the email address.)
5. Close the "Preferences" window and save the changes.
Click the red close button in the upper-left corner of the "Preferences" window. If the "Save Changes" dialog pops up, choose Save.
Outlook
1. 開啟 Outlook 後，按"File"。Open Outlook, Click "File".
2. 按帳戶設定 Click Account Settings.
3. 點選電子郵件帳戶(POP) > "變更"
Select the email account (POP) then click Change.
For Outlook 365 version, tick "Leave a copy of messages on server". Do not tick Remove from server after X day(s).
4.2 其他版本請點撃其他設定 For other version, please click More Settings
到 Advanced 頁，勾選"在伺服器上保留一份郵件複本"，不要勾選超過下列天數後就從伺服器刪除
Click Advanced. Tick "Leave a copy of messages on server". Do not tick Remove from server after X day(s). 
5. 按 "確定" > "下一步" > "完成"
Click OK then Next > and Finish.
IPHONE (IOS 18) Default Mail app
1. 在 iOS 主畫面中按「設定」「Settings」。
In iOS homepage, click "Settings".
2. 將目錄向下拉，點選「App」。。
Scroll down and click "Apps".
3. 將目錄向下拉，點選「郵件」，再按郵件帳戶。
Scroll down and click "Mail", then click "Mail Accounts"
4. 按一下電子郵箱 > 按帳戶設定 > 按進階更改內送郵件設定。
Click your email address > click Account Settings > click Advanced to modify Incoming mail setting.
5. 在POP3 設定 點撃「進階」。
Click "Advance" in POP account Setting.
6. 將以下項目改做"永不"。
Set the circled settings to "Never".
