Hi @Alex Xd ,
Yes, it is possible to simulate the behavior of “reply all” through the Outlook API. You can use the Microsoft Graph API, which includes the Outlook Mail API.
This API allows you to create a draft message in response to an existing message. A similar thread you can refer to: https://stackoverflow.com/questions/41937948/how-to-properly-respond-to-an-email-using-the-outlook-rest-api(Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)
As for the cost, the Microsoft Graph API, which includes the Outlook Mail API, is currently free to use. However, please note that while the API itself is free, depending on the scale and nature of your application, other costs such as those associated with Azure Active Directory or other services may apply. You may want to check the latest information from the official Microsoft documentation or the Azure pricing page.
Please kindly understand that the Outlook tag here we mainly focus on general issues about Outlook desktop client, if you want to know more about the API, it is recommended that you go to the dedicated Microsoft Graph forum to get more professional help.
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