Proton mail app (nonweb)- Does the data stay online and in the mail app (win/linux/...) or just in the mail app?

Proton mail app (nonweb)- Does the data stay online and in the mail app (win/linux/...) or just in the mail app?

I want my mail to still be online and not only on my machine. Is this possible?

When using thunderbird you download your mail and your mail is on your machine and not online (unless you tell it to do otherwise).