I don't think they have to rhyme anymore.

When I went off to train to defend this great country I promised my wife that I would write her every single day. So she got seven letters a week for seven months. There were times that my letters would take on a poetic quality. Not for rhythm but through the cadence and word choice.

Bear in mind I was a newlywed and still caught up in the newness... Oh, and we didn't have email at the time. Had to use something that's now called snail mail. Didn't have computers, and a palm pilot meant something entirely different to us.