Quote:When I am running same application on my development PC it works perfectly, but when install setup on client PC it gives error
That indicates that it is a problem with the client system or it's local network environment.
Quote:I tried disabling anti-virus and firewall but same error.
Disabling is a bad choice. All you have to check is if outgoing packets to port 995 are blocked. But this must be not only done for the system itself but also for the router that connects the system to the net. These routers have their own firewall and routing rules. Some have for example options to allow mail services only for specific domains.
From your description this is the most probable source of your problem: The request is blocked by the router. If the client system is part of larger network (like a company or instution), check if they have a network administrator. If so, contact him.
Quote:I tried using port 587 but gave "Handshake error"
Port 587 is SMTP with TLS/STARTTLS. That is a different protocol so that you get an error. But it tells you that you got at least a connection.
Quote:I have enabled "Enabled POP for all Mail" , and also turned On Allow less secured apps
That does not matter while you get no connection. It is necessary to successfully login and use POP3 with Gamil.