A mail session can be configured via components.xml. Here we tell Seam to use smtp.example.com as the smtp server,

<components xmlns="http://jboss.com/products/seam/components"
        xmlns:core="http://jboss.com/products/seam/core"
        xmlns:mail="http://jboss.com/products/seam/mail">
        
    <mail:mail-session host="smtp.example.com"/>
    
</components>