[retroafroman]

In gmail, I use the 'star' function to mark emails that I need to follow up with. More often than not, I can usually look at the subject line and sender and see if it's something I'll need to reply to, or whether I will need to do something (like an invoice that needs paid, or an email from a friend). If I still need to do something with it, whether I've read it or not, I star it. When I get free time and browse to my email, I'll be reminded I need to do stuff and finish it up. This works because I get a fairly low volume of email. Your experience may vary, especially if you get a lot of stuff to respond to.