All mail out of Sudan was treated as military intelligence under Egyptian army law.

Evidence

Then, in August of 1889, it came to the attention of the Ministry of Finance, indirectly by way of the chief officer of the governorate of Cairo [muhäfazat misr], that Ibrahïm Fawzï had smuggled a large packet of letters and documents out of Omdurman, some of them addressed to different consuls, others to various individuals in Cairo and Alexandria. There was no postage on these letters, and they had been sent from postmaster to postmaster in provinces all the way from Aswan. According to military law governing these regions, any mail out of the Sudan was to be forwarded immediately to the headquarters of the Egyptian army, as it was considered military intelligence. This was lucky for Fawzï, because his letters attracted a lot of media attention. — Eve M. Troutt Powell, A Different Shade of Colonialism_…, 536

Then, in August of 1889, it came to the attention of the Ministry of Finance, indirectly by way of the chief officer of the governorate of Cairo [muhäfazat misr], that Ibrahïm Fawzï had smuggled a large packet of letters and documents out of Omdurman, some of them addressed to different consuls, others to various individuals in Cairo and Alexandria. There was no postage on these letters, and they had been sent from postmaster to postmaster in provinces all the way from Aswan. According to military law governing these regions, any mail out of the Sudan was to be forwarded immediately to the headquarters of the Egyptian army, as it was considered military intelligence. This was lucky for Fawzï, because his letters attracted a lot of media attention. The existence of these letters, most of which were appeals for a larger pension based on his rank of liwä´ as created by General Gordon, reinforced the constant appeals that his wife, `Aisha, had been making to the Ministry of Finance for a larger stipend from the government. — Eve M. Troutt Powell, A Different Shade of Colonialism_…, 536

Categorization

• CANDY: A prisoner escaping Omdurman smuggling unstamped letters postmaster-to-postmaster to prove he’s alive is a vivid, tweetable historical nugget.
• XREF: This mail-as-intelligence rule shows how the Egyptian state treated the Sudan as a military zone under direct control, contrasting with how other colonial powers treated mail traffic.
• corroborated: 2 independent passages support this claim — Eve M. Troutt Powell, A Different Shade of Colonialism_…, 536