Problems saving mail to drafts or sent folder

[fengyau]

Hi,
I've recently installed Mail Toaster and everything seems to be fine.
Created some domains and added for users as per instructions. The only problem I seem to be having is that when someone tries to save their mail to drafts, is that they get an error message saying that there were problems copying to the drafts folder. This happens to a lesser extent when copying mail to the sent folder, but does happen quite often. It doesn't matter which email client is used.

Thanks in advance