The following link might be helpful: https://support.mozilla.org/en-US/questions/1495941#answer-1721871

Although the above link talks about "Sent" folder, I think the concept and steps can be applied to "Trash" folder (which you called deleted folder) as well.

I tried this, simple enough but still the same problem. The deleted files are in fact put in the trash folder on my phone app but they are not moved to the trash folder on the server folder. The odd thing is if i move a file from my inbox to another folder it in fact does move on the server as well.

I have the Tbird app for my laptop and it works perfectly.

Thunderbird Beta 21:29 > Seems to be happening on my Android devices too with IMAP accounts. In some cases I delete an email and then when I refresh it is still there. If I go to my Windows desktop and delete the emails they are gone.