Mails to mail-enabled public folders end up as posts instead of as emails. Can that be changed?

You can change this behaviour in Exchange 2003 by setting a simple registry entry:

Under the registry key HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\Public-<GUID>

you need to create the key "Incoming defaults to IPM.Note" as a DWORD

The value 1 means incoming emails show up as IPM.Note (normal email)

The value 0 means incoming emails show up as IPM.Post (posted object)

The Microsoft Exchange information store service must be restarted after changing the value in the registry.

Thanks to Richard Mastny, LogoiX for notifying us of this solution!