FortiMail is a cloud service while FortiAnalyzer is deployed on-premises

You need to publish FAZ's port 514 UDP through a VIP, and add a firewall rule to allow syslog traffic from WAN to FAZ (with the VIP as destination) from FML IP only.

We are having 2 analyzers in 2 different subnet is this solution durable .

Do you have document for this solution

Your FAZ is behind some sort of Firewall anyways, so just allow one public IP to talk to FAZ over port 514 (udp/tcp depends on what you use).
You'll see an IP of your FCTEMS cloud instance once it starts to log

Thanks for your solution will apply this and update .