如何使用 Linq Outlook C# 从商店中的所有文件夹中搜索电子邮件

Question

I am performing custom action on all incoming replies through VSTO add-in. The add-in will compare ConversationID of incoming reply with existing email. It works fine if I have to search inside one folder but my problem is email can be in any folder in store. Here is my code.

void items_ItemAdd(object Item)
        {
            Outlook.Application application = new Outlook.Application();
            string filter = "RE: ";
            Outlook.MailItem mail = (Outlook.MailItem)Item;
            Outlook.Folder folder = mail.Parent as Outlook.Folder;
            if (Item != null)
            {
                if (mail.MessageClass == "IPM.Note" && mail.Subject.ToUpper().Contains(filter.ToUpper()))
                {
                    var RequiredMail = (from e in folder.Items.Cast<Outlook.MailItem>().OrderBy(X => X.ReceivedTime).Where(C => C.ConversationID == mail.ConversationID) select mail).FirstOrDefault();

                    // Perform custom action
                        }
                    }
                    catch (Exception ex)
                    {
                        MessageBox.Show(ex.Message);
                    }
                }
            }
        }

Also, I have read that searching for an email using Linq is not very efficient. Is there any other more efficient way to get RequiredMail ?

Any help will be highly appreciated.

Thank you.

Answer 1

First of all, you must be aware that ItemAdd event may not be fired if more than sixteen items are added to the collection. This is a known issue in Outlook. The following series of articles describes possible workarounds for that:

• Outlook NewMail event unleashed: the challenge (NewMail, NewMailEx, ItemAdd)
• Outlook NewMail event: solution options
• Outlook NewMail event and Extended MAPI: C# example
• Outlook NewMail unleashed: writing a working solution (C# example)

Mixing LINQ and COM objects is not a really good idea. You should release underlying COM objects instantly to prevent any known issues.

If you need to search for items in all folders you may use the AdvancedSearch method of the Application class which allows to perform a search based on a specified DAV Searching and Locating (DASL) search string.

The key benefits of using the AdvancedSearch method in Outlook are:

• The search is performed in another thread. You don't need to run another thread manually since the AdvancedSearch method runs it automatically in the background.
• Possibility to search for any item types: mail, appointment, calendar, notes etc. in any location, ie beyond the scope of a certain folder. The Restrict and Find / FindNext methods can be applied to a particular Items collection (see the Items property of the Folder class in Outlook).
• Full support for DASL queries (custom properties can be used for searching too). You can read more about this in the Filtering article in MSDN. To improve the search performance, Instant Search keywords can be used if Instant Search is enabled for the store (see the IsInstantSearchEnabled property of the Store class).
• You can stop the search process at any moment using the Stop method of the Search class.

Read more about that in the Advanced search in Outlook programmatically: C#, VB.NET article.