Perhaps the most important question is, what have you configured the add-on to do with the dupes? If you want the dupes to be rid of from the inbox and All Mail folder as well, then you should tell the add-on to move the dupes to the IMAP Trash/Deleted/Bin folder of that account, then follow them in that folder and empty it AFTER reviewing what the add-on moved there.

That sounds like a good idéa. Problem is i can't find that option in the setting for the addon.

This is all the options i can find for the addon.

Perhaps i use the wrong addon or missed some kind of option with the synchronisation.

I could not find this setting in the add-on-setting menu at all. The addon im using is called Remove Duplicate Messeges (Alternate)

Could it also be that i misinterpreted the whole "all mail" directory?

I installed that same add-on, and at the bottom of the dialog that shows the dupes, there are options to either permanently delete those messages or move them to a specified folder. Do you not see the same options? The All Mail folder is where Gmail stores ALL your messages, including sent messages. Everything that's inside the Inbox is actually stored in the All Mail folder. Gmail's system can be quite confusing, but in this case, what you should know is that the add-on by default skips the All Mail Gmail folder when searching for duplicates. So, how are you initiating the search for dupes? Are you right-clicking the Inbox and then select Remove Duplicates?

I rightclick on the all mail icon and seclect remove duplicates. After i find them i choose prem delete, and after that the number in the lower right corner seems to be in order. But if i go to gmai.com and check the total amount of mails inside "all mail" nothing is changed after the duplicate remove.

If i quit/restart thunderbird it all comes back again.

Since i can't post urls to screenhots its a bit hard to explain.

I rightclick on "All mail" and select remove duplicates from the menu. Thats how i start it.

Everytime i restart thunderbird it seems to "fetch" the removed mail back again. Even tho i removed them with addon and picking the delete permanently option. The delete don't sync if i login to gmail thru their own web interface.

Then tell it to move the dupes to that account's IMAP GMAIL>Deleted|Trash|Bin folder. This action will be performed on the server side as well. After that, review the moved items then empty the Trash|Bin|Deleted folder to permanently delete them on the server.

That solved it! HUGE THX Stans!

You're welcome.

Be a bit careful about removing duplicates in Gmail. The Gmail server automatically eliminates duplicate emails from its files and if you have your synchronization settings done properly, you should not have any duplicate email messages in Thunderbird after it has finished synchronizing to Gmail. Gmail keeps all messages in the one folder and then uses "labels" to help you organize your mail. In Gmail, your messages are only stored once with tags in the labels. So if you delete the message from All Mail, you might delete it from Gmail entirely and it would disappear from the label folder as well.

You are 100% correct Kent, that actually happend to me. I had to redo the whole import from outlook .pst files into google again. Luckily i had all those mails as backups but its a very good point which i had to learn the hard way.

Another "bad" thing is that google automaticly flagged almost 700 of my imported mails as spam/trash so its also very good to know and to check there to make sure u don't get important emails flagged.