A program is trying to send an e-mail message on your behalf warning in Outlook

 If you are using a Remote Desktop host and Outlook, you may come across an issue with 3rd party applications trying to send email.

Outlook will give you an warning saying that "A program is trying to send an e-mail message on your behalf"

The quick fix is to add a reg key (DWARD) setting the ObjectModelGuard to 2 as outlined in the following

https://docs.microsoft.com/en-us/outlook/troubleshoot/security/a-program-is-trying-to-send-an-email-message-on-your-behalf

The location changes based on if you have Office MSI, click to run, and 32 bit or 64 bit installed but its also in the following key

Office\<x.0>\Outlook\Security

x being the version of Outlook installed.

If this does not work you can also try the following keys in the same location

"promptsimplemapisend"=dword:00000002
"promptsimplemapinameresolve"=dword:00000002
"promptsimplemapiopenmessage"=dword:00000002
"promptoomsend"=dword:00000002
"promptoommeetingtaskrequestresponse"=dword:00000002
"promptoomaddressinformationaccess"=dword:00000002
"promptoomsaveas"=dword:00000002
"promptoomformulaaccess"=dword:00000002
"promptoomaddressbookaccess"=dword:00000002
"adminsecuritymode"=dword:00000003

But this was the older way to do it and ObjectModelGuard should be the go to at first.

Microsoft Support and Recovery Assistant

 

Microsoft Support and recovery assistant is a nice tool to help with Office applications, Microsoft 365, and Outlook issues.

Its a nice first step if you are having an issue with a device or an account.

https://support.microsoft.com/en-us/office/about-the-microsoft-support-and-recovery-assistant-e90bb691-c2a7-4697-a94f-88836856c72f

Microsoft 365 Office Applications on a Shared computer (EG Remote Desktop Host)

 Microsoft 365 Office application can be installed on to a Remote Desk Host and set to allow shared activation.

This requires the user to have one of the following Microsoft 365 license.

• Office E3
•  Microsoft 365 Business Premium

https://docs.microsoft.com/en-us/deployoffice/overview-shared-computer-activation

You can confirm its worked by going to the following registry key

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\ClickToRun\Configuration. 

There should be a value for SharedComputerLicensing with a setting of 1

https://docs.microsoft.com/en-us/deployoffice/troubleshoot-shared-computer-activation

Downgrade Office 365 Click to Run

First you going to need to know what you are downgrading too.

https://docs.microsoft.com/en-us/officeupdates/update-history-microsoft365-apps-by-date

Once you know the build you want to use:

1. Start PowerShell Elevated
2. Type cd  "C:\Program Files\Common Files\Microsoft Shared\ClickToRun"
3. Type ".\OfficeC2RClient.exe /update user updatetoversion=16.0.<BUILD NUMBER>"

This should then trigger the Office installer which will do the rest of the work.  Once its finished I would open an office application and confirm its worked and then disable updates.

I would not recommend this as a go to fix really if you can help it.  but if you have old add-ins and plugs that are playing up on a newer build and the company is not in a position to get them updated it can help in the short term.

Long Term I would recommend resolving the issue that is that is making you downgrade and then reenable the updates again.