If you are not able to delete the messages from Horde and getting an error :

‘There was an error deleting messages from the folder “Inbox”. This is what the server
said: [TRYCREATE] Mailbox does not exist.’
Product versions this article applies to:

SOLUTION :
Most probalby you have switched your webmail to
“When deleting messages, move them to your Trash
folder instead of marking them as deleted?” in Horde
IMP preferences under “Options” -> “Deleting and Moving Messages”.
Please make sure that trash folder was created and selected under
“Trash folder:” option.