Inbox zero is overrated.
Be your own person. Have a thousand emails in your inbox, or just 5, or wahtever. . .
Be a strong person, just fucking chuck the entire inbox into the recycle bin!
If it is really important you'll get another email about it soon. If not, just deal with the consequences of living under a system that bends instant worldwide near magical means of communication towards endless profiteering instead of building a more connected community