I think it could be how your mailserver handles junkmail. In TB when i rightclick and empty junkmail it dissapear, if I delete it it shows up in trash. As you move it to junk on your mail-server-account it can be how they handles it or how you setup your account on their server.

Thanks for your suggestion @Gnospen. The problem I'm describing doesn't have any relation to junk messages. I've disabled Thunderbird handling of junk mail.

In this case I'm only referring to deleting messages in any folder, or folders as a whole.

In the "Server Settings" tab, in the section "When I delete a message", I only want to use teh "Move it to this folder" option. I've had it like this for many years, and it's only after the upgrade to 31.4.0 that it has stopped working.

Deleting messages works fine from RoundCube webmail in a browser and from K9 Mail on Android, so the issue is isolated to Thunderbird on Mac.

First check that the Trash folder is not full. If it is full you cannot add more trash. Right click on Trash and 'Empty Trash'.

The other thing that I find a bit odd is this: Trash folder is within a folder named [Special]/Trash. Did you create [Special]/Trash? Did you put Trash in that folder?

This Trash folder is within a folder named [Special]/Trash means that you have demoted it to a sub-folder. So, is that Trash sub-folder actually selected as a subscribed and synchronised folder?

suggest you try: Move Trash out of the [Special]/Trash folder. I've never come across someone having a Trash in a Trash. Trash should be on the same level as Inbox, Drafts, Sent, Archives. Other folders that are not sub folders. Although, I have come across some IMAP accounts having everything within an Inbox folder.

Toad-Hall said

First check that the Trash folder is not full. If it is full you cannot add more trash. Right click on Trash and 'Empty Trash'.

Definitely not related to the folder being full, have tested variations around this and nothing changes.

The other thing that I find a bit odd is this: Trash folder is within a folder named [Special]/Trash. Did you create [Special]/Trash? Did you put Trash in that folder? This Trash folder is within a folder named [Special]/Trash means that you have demoted it to a sub-folder.

Yes, I created this folder and configured Thunderbird to use it as the Trash folder.

It's not really so odd. It's a way of organising all "special" folders into a separate space. Gmail does this with the "[Gmail]" folder, in which the Drafts, Archive, Spam, Bin, Important and Starred folders are placed. Thunderbird works fine with this set up, including the Bin (Trash) functionality.

So, is that Trash sub-folder actually selected as a subscribed and synchronised folder?

Yes, it's a sub-folder and it is subscribed and synchronised.

suggest you try: Move Trash out of the [Special]/Trash folder.

Moving it to the top level has worked. I had previously tried this, however it turns out it's necessary to restart Thunderbird after making the changes.

Given this works with Gmail and not with another IMAP client, and that other clients such as RoundCube and K9 also function as expected with the nested Trash folder, I'm inclined to consider this a bug, pending the issue being reproduced by anyone else.

I've never come across someone having a Trash in a Trash.

It's not a Trash inside a Trash. It's a Trash inside a regular folder, that just so happens to have non-alphanumeric characters in the name, which are 7-bit safe, as specified in the IMAP4rev1 protocol RFC3501.

Trash should be on the same level as Inbox, Drafts, Sent, Archives. Other folders that are not sub folders.

Is there a rule to this effect in the IMAP specification? Looking through RFC3501 I see no mention of how folders should be arranged, and am unable to find any other RFC that would suggest such practices either (http://www.imapwiki.org/ImapRFCList).

As mentioned earlier, Gmail has all these "special folders" within the "[Gmail]" folder and all works fine.

Additionally having these "special folders" within the "[Special]" folder works with other clients, such as RoundCube and K9Mail.

Gmail does have it's own method. Typically, all emails are stored in 'All Mail' and labels are applied. Labels being converted to folders to allow that email to appear to show in various folders for IMAP purposes. Not saying they are unique, as I'm not sure of every server, but it may not be the method used by other servers.

I can see what you mean. But I was refering to where Trash would have been expected to be had it not been moved, hence why I asked if this was something created as default by server or whether it was created by you.

I'm glad to hear it is now working ok.