Hello,
With the rule above it just forcing all Mail traffic to go out the WAN with the highest upload. This is only for Mail traffic and all other traffic I.E. web browsing, video… will route normal through all of your available WAN links (Depending on how you have your outbound policy rules setup). If you just want your PC to go out the “High Upload WAN” for mail traffic you can use the same rule above but just put the IP address of the computer/device that you are using in the “Source” portion.
Also, here is a KB article explaining more in depth about Outbound Policy Rules:
http://www.peplink.com/knowledgebase/understanding-configuring-outbound-traffic-rules/