MAPI_E_FAILONEPROVIDER from Redemption

Question

I'm trying to user Redemption to update a user's Outlook contacts. The user I'm affecting is passed in the exchangeUser, call him "Target User". This code works when I run it logged in as myself:

public OutlookFolders(string outlookRootFolder, string exchangeUser, string mailServer)
{
    var session = new RDOSessionClass();
    session.LogonExchangeMailbox(exchangeUser, mailServer);
    session.Stores.FindExchangePublicFoldersStore();
    var store = session.GetSharedMailbox(exchangeUser);
    //...
}

I tried to log in as a 3rd user "Test User" who is not me and is not "Target User". My program brings up a password prompt at runtime when it gets to FindExchangePublicFoldersStore, and if I don't fill in my credentials it fails with the error:

System.Runtime.InteropServices.COMException (0x8004011D): Error in 
    IMAPISession.OpenMsgStore(pbExchangeProviderPrimaryUserGuid):
    MAPI_E_FAILONEPROVIDER
ulVersion: 0
Error: Microsoft Exchange is not available.  Either there are network
    problems or the Exchange computer is down for maintenance.
Component: Microsoft Exchange Information Store
ulLowLevelError: 2147746069
ulContext: 1318

I tried giving "Test User" owner permission on "Target User's" Mailbox and Contacts folder. Doesn't seem to make a difference. What other permissions need to be set for this to work?

Answer 1

The rule of thumb is to run your code as a user who can access the mailboxes in question, call LogonExchangeMailbox for the current user, then open other users' mailboxes using GetSharedMailbox.