A nucleus of Italian air transports were based in East Africa in early 1941.
9 SM73; 9 Ca133; 6 Ca185 (?); 1 Fokker FVII
https://mab.forumfree.it/?t=53052775
I would hazard a guess that the "mailplane" is an SM73. However....
"At the beginning of 1941 – after a few months’ operating schedule was carried out to support the Italian troops in Libya, Albania and Dodecanese – an entire section of SM75s was again brought onto the Benghazi-Gura and Benghazi-Gondar (respectively 2700 and 2800 km long) routes and onto the even harder Benghazi-Addis Abeba and Benghazi-Gimma (respectively 3200 and 3300 km) lines."