Hi
Firstly, the latest 7.x version available is 7.3.1. Check
http://www.wingate.com/showfaq.php?id=33 to find out what changed.
Also, there's no such product as WinGate Mail Proxy, it's just WinGate.
In terms of support, there's product support (e.g. our support desk will still answer questions), and then there's updates / bug fixes.
We've ceased active (new feature) development on the 7.x branch, since 8.0 came out nearly a year ago. We haven't had any reason to release a maintenance release either. Having said that, it's hard to predict the future, so if something came up that needed urgent addressing, and a significant number of people were affected, we would release a maintenance update to 7.3.1 if we couldn't convince affected parties to update to the current version.
Keeping software maintenance (version protection) up to date means you're always eligible for the latest version. That will generally be the one we are focussing on in terms of maintenance issues (bug fixes), and definitely is the target of new features.
In terms of plugins like Kaspersky AV for WinGate, sometimes an update for WinGate is released that requires also updating the plugins as well (e.g. if there is a change to an interface that the plugin uses to work with WinGate). So pretty much everything comes back to the WinGate life cycle.
So to finally get to your specific questions, we don't have a fixed date for end of support for WinGate 8 or WinGate 7. We still provide technical support for users back even to WinGate 5 (although it's been a long time since we were asked any questions by anyone running that). That was released over 11 years ago. I don't know if this is helpful. Our main support policy is to help all-comers no matter what.
Regards
Adrien de Croy