[Dovecot] ":" in filenames

dovecot seems to have an issue with :'s in pathnames: imap(test.user): Fatal: Failed to create storage with data: /home/ hosted/example.com/users/test:user

This causes a bit of a problem with vmailmgr since it, by default, replaces .'s in maildir path with :'s. I'm curious as to why :'s in paths are an issue? Do they have special meaning to dovecot?

Lars Hansson