Originally Posted by till
If you want to use maildir, you will have to do 2 steps:
1) Install a maildir capable pop3 and IMAP daemon like courier.
2) Switch to maildir in ISPConfig under management > server > settings on the mail tab.
But be aware that all emails that have not been fetched by your customers from their mbox files will be inaccessible after the change.
mmm ok, ill take it as last resource...