Symptom

You are no longer able to delete a message from the Inbox folder in Horde webmail.

You receive the following error message:

Horde webmail error: 'There was an error deleting messages from the folder "Inbox". 
[TRYCREATE] Mailbox does not exist.'

Solution

Most likely, you have switched to using the setting "When deleting messages, move them to your Trash folder instead of marking them as deleted." This can be found in Horde IMAP preferences under "Options" -> "Deleting and Moving Messages". See Figure 1 below:

Figure 1

Please make sure that your "Trash" folder was created and selected under the "Trash folder:" option first.