When people reply to a Google+ post of mine or mention me, I get an email. On at least one of those emails, I was able to reply via email. That doesn't seem to be working any more and now messages say "you can't reply to this email". Is there a way to restore this functionality?
You should be able to reply to the comment right within the email message.
Gmail and Google plus just got a little closer, with the search giant announcing that you can now use Gmail to respond to Google plus notifications.
The changes mean that Google social’s networking site which has already been integrated into search results, will also become an important part of Gmail.
So what will it mean for users? Well they can reply to Google plus notifications instantly from their Gmail inbox without having to click on the Plus icon on the Google bar.
More at the official announcement: http://googleplus-update.blogspot.com/2012/05/now-reply-to-google-plus-comments-from.html