Message Class of received email in outlook is IPM.NOTE

StackOverflow https://stackoverflow.com/questions/21667304

  •  09-10-2022
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Question

I have a VSTO outlook add-in which specifies that the message class of my outbound mail to be IPM.Note.Secure.

However , when the email reaches the inbox of the recipient , the message class changes to IPM.Note instead.

I have checked my sent items and the message is indeed sent with a message class of IPM.NOTE.Secure.

Please advice if there's any steps that i should take note of when changing the message class .

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Solution

PR_MESSAGE_CLASS is a MAPI property, it will be lost when the message is converted to MIME when it is sent through an SMTP server.

You can force Outlook to send in the RTF format (the infamnous winmail.dat file) which will preserve all transmittable MAPI properties. Try to set the UseTnef (DASL name http://schemas.microsoft.com/mapi/id/{00062008-0000-0000-C000-000000000046}/8582000B) property using MailItem.PropertyAccessor.SetProperty.

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