Whenever you have an important email you need to address and can’t get to it right away, after reading it mark it as unread. Most email clients have some way for you to “flag” messages a being important or needing a follow up, but nothing stands out more than seeing you have unread messages.

Additionally, if you use a special folder orginization for your emails, make sure the most urgent remain in your inbox so you will be constantly reminded they need to be addressed.

Of course come up with a system which works best for you, as the mark as unread works best for me.