Railway Mail Service through Alpine Tunnel?

I am trying to find out if there was ever a mail contract for service through the Alpine Tunnel to Gunnison. I have found that RPO service was run over the C&S from Denver to Leadville and Silver Plume, but I have not been able to turn up anything for the C&S line to Gunnison. I am wondering if there was no contract on this line as it might have duplicated the service of the D&RG, who did have a mail contract to carry mail over Marshall Pass to Gunnison, Montrose, etc.

If you know of such rail mail service through the Alpine Tunnel, what was the RPO cancellation?-- "Denver & Gunnison"? "Como & Gunnison"?