dsn=4.0.0, stat=Deferred: Connection timed out with outlook-com.olc.protection.outlook.com.

The best thing to start with is to run a packet capture on the destination IP and look to see if you are actually receiving a response from the server on the WAN side.

You can also run a diag debug flow trace to monitor that traffic and see what the fortigate is doing with it.

Outside of those two steps, opening a TAC case would be a good step as well.

OK, Thank you