Which Outlook MailItem properties are visible by recipient

WHILEY, Sai 1

We are working on email integration with an in-house .NET application using the Outlook MAPI,
and would like to tag mail with a reference that is readable by the sender and recipient clients, and is retained forwarding and replying.

Is there a list available of _MailItem properties that are both transmitted and writable?
Ideally we would like this to be a field not visible in UI so that users cannot clear or overwrite the tag - such as a hash in the subject or body

Thanks very much,

JeffYang-MSFT 6,241 Reputation points Microsoft Vendor

2021-04-12T08:44:06.043+00:00

Hi @WHILEY, Sai ,

Welcome to our forum.

Sounds like you are sending emails using programing methods instead of using Outlook desktop clients, right? If yes, please kindly understand that the Outlook tag here we mainly focus on general issues about Outlook desktop client and know little about programing. I tried some search and found the list of _MailItem Interface, please check if it could help.

By the way, in order to better help solve your issue, I removed the Outlook tag and added some programing-related tags here, so that other partners who read the forums regularly can either share their knowledge or learn from your interaction with us. Thanks for your understanding and hope your issue could be resolved soon.
WHILEY, Sai 1 Reputation point

2021-04-12T23:57:10.16+00:00

Hi @JeffYang-MSFT , thank you for that, and your advice around the Outlook tag
I have already had a look at the _MailItem interface, but I appreciate the effort :)
Danstan Onyango 3,821 Reputation points Microsoft Employee

2021-04-14T07:24:01.43+00:00

Have you had a look at using MS Graph Adding custom data to resource using extensions and Outlook extended properties

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Which Outlook MailItem properties are visible by recipient

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