In Outlook, you can set the client on one device to be the ONLY ONE that can physically delete messages on the server. All others clients can be set to only delete messages locally. Outlook users like me, mistakenly look at the server settings in Thunderbird and assume that it works the same way. IT DOES NOT. When I see the option "Don't delete any messages", I assume that its only talking about DELETED messages. IT IS NOT. So when I deleted all the messages I'd read on my phone to save space, they ALL went "poof" on the server, and I lost many threads that I desperately needed on my computer at work.
Why would you ever want to delete messages from the server that are still un-deleted in your inbox? Are there people who really want all of their mail stored locally, scattered between all of their devices?
Here's a better idea. Do it like Outlook does, or at least give us the option to do it that way. Give us options that say:
"Don't permanently delete any DELETED messages from the server".
"Permanently delete all but the most recent [number] of DELETED messages from the server"
"Permanently delete all DELETED messages older [n] days from the server"
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I must assume this is some sort of functionality that is provided by the exchange server platform that outlook was written specifically to interface with. My understanding is there is no concept in the IMAP specification for one client to be in some way special from others that access the account. You have access to the mailbox, or you do not. Fine grained access like the ability to move or copy or delete is just not in the email specification. See https://www.rfc-editor.org/rfc/rfc9051 for the open standard all IMAP mail clients work with.