There’s a post office in Terminal 1 pre-security on the ground floor, close to the center of the terminal. Look for “Poste Italiane”.
The airport map might be a better idea to locate the post office (though it’s interactive and slow).
Robert was kind enough to send a photo (and a postcard!) from MXP. The post office has two outgoing drop boxes; use red for domestic and blue for international. Double-check before posting into the box!
Last updated 22 November 2021