What starts with E ends with E and only has one letter in it?!

What starts with E ends with E and only has one letter in it?!
What starts with E ends with E and only has one letter in it?!

I believe the answer is an envelope. Coincidentally, Caroline Cox of the NYT wrote a column this weekend about how recipients still value a card more than an email. So, despite the convenience of texts and emails, keep stuffing those envelopes.