Originally Posted by Johntpt

The initial question was does anyone know of performances or recordings using a posthorn, and that has been answered. About which instrument did Mahler write for, this is what conductor Ben Zander writes in the liner notes to his recording:

"The three-valved post horn in B-flat used on this recording was found in a shop in Vienna and is an exact replica of an instrument in the Austrian Musical Instrument Museum that would have been in use at the time of the symphony's compositions. In the autograph score of 1896 Mahler's word "trumpet" is scratched out by the composer and the word Flugelhorn is clearly legible. "Der Postillon" (mailcoach driver) and "wie die Weise eines Posthorns" (in the manner of a post horn) appear above the solo. The first edition indicated Flugelhorn for the solo, but all later editions call for the Post horn. So, it appears that at some point in between, Mahler changed his mind."

The music is clearly written for a valved instrument as the chromatic notes could not have been played on a valveless instrument, say the one written for in Mozart's Posthorn Serenade.
JU