I am unclear on your problem. If a POP account, the only folder you can download is the inbox folder.

It's unclear what you mean, but it looks like you're referring to being able to see in Thunderbird Sent messages stored on the server (not "outbox", which is something else).

What type of mail account is this (POP, IMAP)? Which is your mail service provider (in case it has some particularities)? And what are your account Copies & Folders settings for saving sent messages?

Hi David

Thanks a lot for your reply and your support.

All server accounts are setted as POP because I need all messages offline for archive purposes and I don`t need to sync which would imply, for example, that also delete would apply synchronized.

The concerned email providers are gmail and gmx.

Again, thank you very much for your kind assistance.

The problem with POP is what david said, that you only have access to the server Inbox that way, not to any other folder on the server such as Sent. You may tell Thunderbird to keep a local copy of the messages it sends (in the account Copies & Folders settings), but that will be a separate (local) folder, independent of the folder used to store sent messages on the server, meaning any messages sent using any other device or application won't appear there…

You are wanting all messages both online and offline. You need IMAP to access all messages. If the purpose of having on PC is for backup, then you need to ensure all headers and messages are local daily (file>offline>download) and then copy elsewhere daily. I encourage you to rethink what your goal is, as that is a lot of effort.

Don't know whether this still works the same (it's been years since I stopped using POP for Gmail), but forgot to mention that Gmail used to make messages sent with webmail available for download to the POP mail client as if they were received messages. Although this may seem weird, it allowed storing all sent messages locally in the mail client regardless of whether they were sent with webmail or with the mail client.

Thank you guys !

But how I could change from POP to IMAP without loosing the already arranged folder order of 9k imported emails by 4 different email accounts?

Since the first and last time when I tried out the different TB import options, I had to import everything again because TB setted up the email accounts completly new.

Again, thnx a lot for your advise !

Not sure this will answer all your questions, but it should get you started. Ask if you need clarification or have further questions not addressed there:

https://support.mozilla.org/kb/switch-pop-imap-account

I guess, step no 2 "deactivating the POP-account" confirms that TB sets all accounts back.

Don't know what you mean by "setting all accounts back". Step 2 does what it says it does, i.e. stop downloading messages with the old (POP) account so it's only the new (IMAP) account that checks for mail on the server from now on, but you may keep both accounts active and continue downloading mail with the POP account if you prefer. Just keep in mind that what you do in one of the accounts may affect what happens on the other if you do that.