How to get the sender e-mail address associated by the folder item? (vsto / outlook 2010 / mapi)

Question

I have in my Outlook 2010-Add-In (c#) many folders. They are in my private post box or in one of my shared post boxes.

Now I am looking for a solution to find out, how to get the right email address (sender / recipient) associated with a dedicated folder. It could be any folder from my private or anyone of my shared post boxes.

I think, maybe I could use the EntryId / StoreId from the folder item to identify the corresponding email address.

I know already, that I could get the email address from any mail item but I'm not looking for this solution.

Answer 1

I like to answer my own questions: I think that I've found a plausible solution.

I do not treat any exceptions inside the function, I do that from outside.

private string GetSMTPAddressByFolderItem(Outlook.MAPIFolder mapiFolder)
    {

        string PR_MAILBOX_OWNER_ENTRYID = @"http://schemas.microsoft.com/mapi/proptag/0x661B0102";
        string PR_SMTP_ADDRESS = @"http://schemas.microsoft.com/mapi/proptag/0x39FE001E";

        Outlook.Store store = null;
        Outlook.NameSpace ns = null;
        Outlook.AddressEntry sender = null;
        Outlook._ExchangeUser exchUser = null;

        try
        {
            if (mapiFolder == null)
            {
                return null;
            }

            // Get the parent store.
            store = mapiFolder.Store;

            string storeOwnerEntryId = store.PropertyAccessor.BinaryToString(store.PropertyAccessor.GetProperty(PR_MAILBOX_OWNER_ENTRYID)) as string;
            ns = Application.GetNamespace(Constants.OL_NAMESPACE); // i.e. "MAPI"

            sender = ns.GetAddressEntryFromID(storeOwnerEntryId);

            if (sender != null)
            {
                if (sender.AddressEntryUserType == Outlook.OlAddressEntryUserType.olExchangeUserAddressEntry ||
                    sender.AddressEntryUserType == Outlook.OlAddressEntryUserType.olExchangeRemoteUserAddressEntry)
                {
                    exchUser = sender.GetExchangeUser();

                    if (exchUser != null)
                    {
                        return exchUser.PrimarySmtpAddress;
                    }
                    else
                    {
                        return null;
                    }
                }
                else
                {
                    return sender.PropertyAccessor.GetProperty(PR_SMTP_ADDRESS) as string;
                }
            }

            return null;
        }
        finally
        {
            if (ns != null)
            {
                Marshal.ReleaseComObject(ns);
                ns = null;
            }
            if (store != null)
            {
                Marshal.ReleaseComObject(store);
                store = null;
            }
            if (sender != null)
            {
                Marshal.ReleaseComObject(sender);
                sender = null;
            }
            if (exchUser != null)
            {
                Marshal.ReleaseComObject(exchUser);
                exchUser = null;
            }
        }
    }