When setting up Maximizer to communicate with your e-mail system it is important to understand what it can and cannot do.
In and of itself Maximizer possesses no e-mail capability at all, all the functions you see it do are managed by calling various aspects of your existing e-mail system through the MAPI.
So while you cannot set Maximizer up to communicate directly with GMail (as it has no POP client to manage the communication), you can setup a POP client on your machine to talk to GMail and then as long as the POP client is one of the e-mail systems Maximizer works with you will be able to access your GMail via POP3.
