Agree that it is a subject of interest, perhaps a collaboration can be arranged among those interested in better understanding the Mail Service. My focus is the Gettysburg campaign and I working to identify mail carriers, post offices, postal officials, gather data on delivery times, etc. In the Army of Northern Virginia, mail seems to have been sorted mainly by brigade (infantry). In the regiments a postal clerk or the Quartermaster would become involved in the distribution process. Winchester was an important mail hub; stage coaches carried it up the Shenandoah Valley until Federal incursions ended the practice. Wagon transport or individual designated carriers took mail to the army on the march, although the latter were vulnerable in hostile territory. On 8 July 1863, the mail for McLaw's division was captured by Federal cavalry. But otherwise delivery was relatively reliable and timely considering the era. Chaplain Betts of the 30th NC once found that the postal clerks were holding up printed materials for his regiment and he complained to the Postmaster, who acted swiftly. Afterwards a number of angry clerks confronted the chaplain; they feared being sent back to the ranks. Newspapers appear to have been handled separately, and these were often delivered by young blacks. Boxes with food and clothing from home were also sent, but it's not clear to me if the postal service handled boxes - they were hand carried by army chaplains and soldiers returning from furlough. In the Federal army, mail was stopped for two weeks or longer when Lee invaded the north. On 5 July 1863, the Union Second Corps had 28 large mail bags waiting for them at Taneytown. Friendly citizens along the march route often volunteered to accept mail from passing soldiers, promising to take them to the local post office for onward delivery. Although a risk, extant cases show they kept their word.