GMAIL will treat you nicely if you comply with their sending rules. These include not sending too much mail at the same time. Our Ironport appliance takes care of that with automatic throttling at the machine level but there are few more considerations.
One such is the GMAIL feature called GMAIL Unsubscribe. Its a sender setting in GMAIL that will help your email sending reputation. Previously, some GMAIL users would click on report spam instead of clicking on the unsubscribe link in your newsletter -bad news for your email reputation.
Now, when coded correctly, GMAIL provides new options to make it easier for users to unsubscribe from your newsletter -instead of damaging your reputation.
Of course with our platform, we can see who clicked on the report spam button and we automatically unsubscribe them. That way you avoid getting penalised by GMAIL by sending email to those who clicked "Report spam" but did not select the unsubscribe option...
However there are some preconditions for this to work, so its not for everybody and not for every email platform.
Hotmail has had a similar feature since 2006 but handles it in a different way. In Hotmail, the LIST-UNSUBCRIBE format must be a link which will opt out the contact; GMAIL requires MAILTO to be specified inside the LIST-UNSUBSCRIBE. So your email platform will need to cater for the different unsubscribe formats of both.