Get Unique Id From MailItem (Microsoft.Office.Interop.Outlook)?

Question

I'm creating an application that is reading emails received in outlook.

The reading process is something like this:

using Outlook = Microsoft.Office.Interop.Outlook;

var app = new Outlook.Application();
var ns = app.GetNamespace("MAPI");
ns.Logon(null, null, false, false);

var inboxFolder = ns.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderInbox);
var subfolder = inboxFolder.Folders["MyFolderName"];

foreach (Outlook.MailItem item in subfolder.Items)
{
    // do something
    // item.EntryID
}

I need to get an unique ID for every item in the foreach loop.

There is a EntryID property in Outlook.MailItem that I used and it was working well, but I found out there was a problem with that property: Whenever I moved the email to another folder (inside outlook), This property EntryID changed.

I ran several tests and discovered that the EntryID value changes only a few chars when I move the mail to another folder.

I need an ID that would be unique no matter what folder. Is there an another property from Outlook.MailItem or any substring of EntryID that is always unique?

I'm using:

• .NET 4.0;
• Outlook 2010;
• Microsoft.Office.Interop.Outlook.dll version 14.0.0.0.

Answer 1

There is no such property. You can create your own property using MailItem.PropertyAccessor or MailItem.UserProperties, but it will stop being unique if a message is copied to another folder as you will now have 2 items with the same id.

Answer 2

Unique Id for MailItem can be obtained by combining few email properties that could unlikely be the same for any different emails e.g.

$"{item.SenderEmailAddress}-{item.SentOn.Ticks/TimeSpan.TicksPerSecond}-{item.Size}";