Should I put my email server in a public subnet or put in a private subnet and use load balancing / routing to route traffic from the internet?

I have 3 subnets setup in a Amazon VPC: public, private application, private database. My web servers are currently in the private application subnet and use a NAT Instance to see the internet.

I need to setup a Win 2012 mail server that will also be used for Jabber and other services. I was hoping to use the same setup as the application servers so that any websites on the mail server will use a Elastic Load Balancer to add a public address and then I was thinking to add a ENI with public address for the mail IP and a 2nd address for Jabber.

I wanted to keep it more secure by placing it in the private subnet, but if the general rule is to put them in public subnets, then I will consider that.