Following the fall of Vicksburg, the CSA, mail delivery from the eastern CSA states to points west of the river became much more difficult. On May 1, 1863 a bill establishing an Express mail across the river was signed by President Davis. Initially the rate was set at 50 cents, and later reduced to 40 cents.
In his studies on the Transmississippi Mail (The Trans-Mississippi Mails After the Fall of Vicksburg,1984, Addendum, 1986), Richard Kruger had this summary of all Transmississippi covers, including stamps on piece:
From the West of the Mississippi, 30 covers/pieces.
From East of the Mississippi: 86 covers/pieces.
Total Covers carried in the Transmississippi Express reported by 1986: 116.
Interestingly, Camden Arkansas was a postoffice designated as a "safe, convenient and accessible point" for the collection of Transmississippi mail (Kruger, p15).
The tables below show the covers moving to and from Arkansas. Additionally, covers carried by private courier companies addressed to or from Arkansas are also presented, although these were not part of the Official Express system. As a group, the two reported west to east covers from Arkansas are the rarest of all CSA classification from Arkansas.