MAPI not launching New Outlook as default MailTo client (C#)

Question

I have some code that uses MAPI to launch the default email client. However, when the default MailTo client is set to New Outlook, MAPI launches the old Outlook client instead. This is causing the programme to hang/crash when used on a new machine that doesn't have old outlook installed.

I am using Outlook version 1.2024.403.300, with Client version 20240329006.06. The installed Mapi dll is Mapi32.dll.

This seems to be a problem with MAPI itself, as when I launch MailTo directly, e.g.

Process.Start(new ProcessStartInfo{ FileName = @"mailto:[email protected]", UseShellExecute = true });

new outlook launches without issue. Unfortunately using MailTo directly is not an option as we need to add attachments to the email, and my understanding is that this isn't supported by MailTo.

Answer 1

The New Outlook does not support MAPI (by design), that is why the old Outlook launches.