Hi! Answering your AI question:
It depends on the type of email. If you have a Microsoft email, or an IMAP email with your own domain, the emails are saved in the cloud and only a portion of the emails are downloaded. You can adjust this in Files > Account Settings > Account Name and Sync Settings > Download email for the past.
If your email is from your own domain but uses POP, it's usually saved on your computer, typically in Documents > Outlook Files.
Regarding the speed test:
Your computer's bandwidth usage should not be the same as the speed test result. The speed test shows the total bandwidth your computer CAN receive, but your computer may not necessarily use all of the available bandwidth, especially since other devices in your home share the bandwidth.