I think I'm doing things backwards

So, I've been coveting a gorgeous cover that Garrett Leigh made for the longest time. The Heart of a Cowboy. I wanted that cover so badly but I had no story for it. Then Garrett had a sale on her pre-made covers and yes, my cover (what, it was mine regardless that I didn't own it. It owned me!) was in that collection for sale. No! Someone would buy it for sure!
Yes, we know how this story goes. I bought the cover, story or not I couldn't stand the thought of another story coming out with my cover. racking my brains I remembered a long forgotten historical western that I'd written about a pony express rider and the ranch owner who loves him. It's old and rough and needs lots of work (did I even know about POV back then? Head hopping, like, woah!).

However as much as I love the title Garrett gave the cover I don't think it will suit this story. I'd like the focus to the title to be the Pony Express rider, but what if the story doesn't pan out and I'm left a book cover that I can't use.

The working title for the story is The Mail Must Go Through. This is the Pony Express motto. PE riders were called Messengers.

Can anyone help me with a title?