If you want to set different mail servers for each of them,then fo gor the way 2.
That's a fairly broad statement - can you elaborate?
mail1, mail2, and mail3 will all be on the same physical server and each will be a VirtualMTA that are then pooled together. In other words:
<virtual-mta mail1>
smtp-source-host 111.111.111.111 mail1.mydomain.com
</virtual-mta>
<virtual-mta mail2>
smtp-source-host 122.122.122.122 mail2.mydomain.com
</virtual-mta>
<virtual-mta mail3>
smtp-source-host 133.133.133.133 mail3.mydomain.com
</virtual-mta>
<virtual-mta-pool general>
virtual-mta mail1
virtual-mta mail2
virtual-mta mail3
</virtual-mta-pool>