[Dovecot] ":" in filenames

[Lars Hansson]

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?

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Lars Hansson