Leave massage copy on server

Dear 雅哉 山田,

Welcome to Microsoft Community.

According to your description, you want to save a copy of the mail on the server.

First of all, I want to tell you that if you use a Microsoft domain email account (@Outlook.com, @Hotmail.com, @live.com, @msn.com), and your Microsoft domain email account is an Exchange account, By default, a copy of the message is saved on the Outlook server (Outlook.live.com)

If you use an email account with a third-party domain name, and your email account is configured as IMAP, the email will first arrive at the server of your corresponding email domain name, and then Outlook will synchronize with the server of your corresponding email domain name to synchronize the email to Outlook.

If you have your email account configured as POP in Outlook, you can go to File > Account Settings > Account Settings in Outlook. Under the email, select your POP account and click Change - More Settings, then select Advanced options. On this page, you will see an option: "Keep a copy on the server", select this option. If your mailbox is not configured as POP, this option does not exist.

I hope this information has been helpful. If you have any questions, please let me know and I will be happy to help you further.

Have a good day.

Best Regards, 

Jim - MSFT | Microsoft Community Support Specialist