At 70 Viale dei Mille, Milan, in 1926 and 1933.
The firm operated from 1911 to approx 1943. Typically it produced illustrated cards by artists, art deco scenes or children, in sets of 4. Early cards had the full name, then around 1922-23 the degami logo was introduced (DE-GA-MI). DGM must also be one of their logos. It quite likely produced cards with other logos,see below). There is an article on this firm in the Italian Wikipedia at it.wikipedia.org/wiki/Degami. It also collaborated with other publishers, for example there are cards with on the adddress side a degami logo and the Primus heading; these were printed in Italy and circulated internationally.
DGM 447M-2 is a half-height card, marked "IMPRIMÉ". Was this an experiment in using the cheaper printed-paper rate for smaller cards? It looks like an export card, so that wouldn't work. The illustrator is Giovanni Nanni (1888 - 1969).
Also see the entry for the logo G.d'A. M. Is this a coincidence or is this an earlier firm of these two?
Dell'Anna and Gasparini 458-1 plus the reverse of another card to show the stamp box.
DGM 143-3
degami 681
degami 1034
degami 1140
DGM 447M-2 rev