I have been able to add items in Context Menu of Excel 2010 cells by the following article.

Is there similar way to do it for Outlook 2010 messages?

https://msdn.microsoft.com/en-us/library/office/gg469862(v=office.14).aspx

Hi,

Please have a look at the following articles and check if they are what you want:

https://msdn.microsoft.com/en-us/library/bb176426(office.12).aspx

http://blogs.msdn.com/b/pareshj/archive/2010/08/06/customising-context-menus-in-outlook.aspx

Since this issue is more related to Outlook development, if you need further assistance, I'd recommend you post a new question to the Outlook for Developers forum:

https://social.msdn.microsoft.com/Forums/office/en-US/home?forum=outlookdev

The reason why we recommend posting appropriately is you will get the most qualified pool of respondents, and other partners who read the forums regularly can either share their knowledge or learn from your interaction with us. Thank you for your understanding.

Steve Fan
TechNet Community Support