ok thank you for confirming, I needed to be sure before proceeding.
The issue then is the filemaker programs code is not emailing correctly, as all your outlook settings are correct.
It is doing this as it is using the DoCmd.SendObject function.
This is a common issue, and there is an Add-in that stops the warning from appearing.
It is called Bells & Whistles for Outlook.
It is not free, but it is the only software capable of doing this.
There is a demo, so you can see it work, and it can be downloaded and installed from my link belowClick Me To View
Once installed, start Outlook, open the Bells & Whistles Options menu located on your Outlook toolbar area, go to the Outlook Tweaks tab and mark the option “Auto-confirm Outlook security warning messages”
If you have any difficulties at all, please do not hesitate to let me know so I can assist you further