District of Douai
The district of DOUAI had 10 post offices between 1852 and 1876. Most of them were head post offices for most of this period. Linear stamps (this also applies to the Nord in general) are very difficult to find in association with the small numeral cancels.
Note the numerals 3451 (used previously by SOULTZ) associated with type 18 of MONTIGNY EN OSTREVENT. Very rare.
Types 22, 24 and 17 from FLINES LES RACHES are difficult to find.