Some customers will use third party applications that integrate with Outlook, and may result in this message continually popping up. One solution is to create a GPO to prevent this:


Outlook 2016 - Allow Applications to send Mail without Warning (Requires 2016 Office ADM files)

    

a.      Create new GPO Under the OU with the desktops in:  "Allow App to Send Mail - Outlook 2016"

                                i. You will need to first import ADMX files onto the servers' policy definitions directory. The appropriate ADMX files are found in the PHL ISO (just mount to the server that you are on from vCenter) -found in EN-US/ GPO/ADM FILES/Office2016/32bit/ADMX.   

                                ii. Copy appropriate ADMX files from here into %systemroot%\policydefinitions.

b.      Right-click the GPO that you created for the group policy settings and select Edit.

                                i.          User Configuration -> Policies -> Administrative Templates -> Microsoft Outlook 2016 -> Security -> Security Form Settings

1.      Outlook Security Mode: Enabled

a.      Outlook Security Policy: Use Outlook Security Group Policy

                               ii.          User Configuration -> Policies -> Administrative Templates -> Microsoft Outlook 2016 -> Security -> Security Form Settings -> Programmatic Security

1.      Configure Outlook object model prompt when sending mail: Enabled

a.      Guard Behavior: Automatically Approve

2.      Configure Simple MAPI sending prompt: Enabled

a.      Guard Behavior: Automatically Approve

                              iii.          User Configuration -> Policies -> Administrative Templates -> Microsoft Outlook 2016 -> Security -> Security Form Settings -> Custom Form Security

1.      Set Outlook object model custom actions execution prompt: Enabled

a.      When executing a custom action: Automatically Approve