Do you remember Exchange 5.5? Where messages that were delivered to Public Folders had the same message class (IPM.Note) as messages delivered to mailboxes? Ahhh – that was nice.

How about how Exchange 2000 changed it so that messages from the Internet to mail-enabled Public Folders defaulted to a message class of IPM.Post? I thought I'd blogged about this before, but apparently not. For those not aware of this, a quick overview is that Public Folder functionality changed with Exchange 2000. Messages sent internally to a mail-enabled public folder retained the message class of IPM.Note (standard message class), but any messages sent from an outside source were converted to a message class of IPM.Post (Message Post class), which causes some issues for clients attempting to reply to those messages, especially from OWA (there is no reply functionality). Outlook seems to handle it better (or at least Outlook 2007 does) and still gives you the ability to reply to a post within a public folder.

Microsoft released a KB article that addressed this issue (I think a lot of people complained about it…) in KB 817809, which allows you to basically set a registry value on your server, and change the behavior back to what many people would consider "normal" behavior, by modifying the PR_MESSAGE_CLASS field and changing it back to IPM.Note. This helps Outlook clients (and OWA clients for that matter) in that items now appear as messages instead of posts, but OWA still has a major problem in that you still can't reply or forward those items. The jist of it is that in order to reply or forward items in public folders in Exchange 2003, you need to have a Front-end server deployed. See http://support.microsoft.com/kb/822178 for details on the requirements to use different features in Exchange 2003.

Bottom line here is that if you require the functionality of being able to reply or forward messages (ipm.post or ipm.note) other than "Post reply to this folder", then you unfortunately have to deploy a Front-end server. At least one bit of good news is that with Exchange 2003, you can use Exchange 2003 Standard edition for that Front-end server, instead of having to use Enterprise edition (as Exchange 2000 Front-end servers required).