You cannot download messages labeled as Spam or sent to Trash. In Gmail, messages marked as spam are sent to Spam label and cannot be read via POP. Messages sent to Spam or Trash are deleted in 30 days, so you need to open these labels regularly on your browser.
As you download all messages in POP, they will take up your disk space.
If you use IMAP, you can sync and read your messages and settings on any of your devices in real time. You can also read messages marked as spam.
Note that you can download up to 1,250MB per day in POP. Exceeding this limit, as you may when you set up a POP connection for the first time, may lock you out of your account. Learn more on Google Workspace Admin Help.
If you'd like to use POP nevertheless, follow the steps below.
1. Open KUMail on your browser and see how much your KUMail data adds up.
Note: If it amounts to over 1,250MB, your account might be locked.
2. Create an app password for KUMail.
3. First, set up the POP settings in Gmail.
3-1. Sign in to KUMail (Gmail) and click Settings (gear icon).
3-2. Click See all settings.
3-3. Open Forwarding and POP/IMAP.
3-4. In the POP download section, choose Enable POP for all mail or Enable POP for mail that arrives from now on.
3-5. At the bottom of the page, click Save changes.
4. Then, open your email client and configure the POP settings as follows.
Incoming (POP) mail server: pop.gmail.com
SSL connection: Yes
Port: 995
Outgoing (SMTP) mail server: smtp.gmail.com
SSL connection: Yes
TLS connection: Yes (if available)
Authentication: Yes
TLS/STARTTLS Port : 587
Account name/user name/email address: Your KUMail address (xxx@kyoto-u.ac.jp)
Password: Your app password (which you created in the step 2)
Note: If you already have other accounts in your email client, be sure to add KUMail as a new, separate account to prevent trouble.