The Aerotarg company, following an agreement by them with the Polish Ministry of Post & Telegraph, issued these stamps. It was agreed that in addition to the normal express postage rate, payable by the use of normal Polish stamps, there would be an additional payment for airmail, payable by the use of the Aerotarg stamps. The agreed rates for airmail were:

letters up to 20gm - 25mk
letters up to 250gm - 100mk
postcards - 25mk
printed paper up to 250gm  - 100mk
printed paper up to 1000gm - 200mk
commercial papers up to 1000gm - 50mk
parcels up to 1000gm - 200mk 
     and for each additional 1000gm - 100mk
registered letters - 400 mk plus 200mk for each 1000mk declared value

The agreement was for the period of the Poznan Trade Fair in 1921 on three routes:
Poznan - Warsaw and return
Poznan - Gdansk and return
Poznan - Lodz and return
No flights were made between Poznan & Lodz either way. 

Although genuine covers are known from Poznan to Gdansk, none are known for the return trip. It is not known for certain if any mail was  actually carried on the return flights.

The first flights from Poznan to Gdansk and from Poznan to Warsaw were on 29 May 1921 The first return flight from Warsaw to Poznan on 31 May 1921. Then there were daily return flights till 16 June 1921 inclusive. Plans to continue these flights were not realised. Postmarks after 16 June 1921 are forgeries.

The stamps were designed by Wilhelm Rudy (hence the initials W.R. on the stamps). The 25mk value shows Icarus against a silhouette of Poznan and the 100mk shows a Junker F3 dropping mail over Poznan. Below each stamp was an advertising label, inscribed T.A.B.R.O.M.I.K., for a vodka factory TAdeusz BROnislaw MIKolajczyk who provided the labels free of charge. The 25mk is printed in black & reddish brown and the 100mk is printed in black and blue. The stamps were perforated 11¼ all round and between the advertising label and the stamp. The stamps were roughly lithographed and many small defects in printing may be found.

The stamps were sold in post offices Warsaw 1, Poznan 1, 3 and 9. In accordance with the agreement the normal postage stamps were postmarked with the post office postmark. The Aerotarg stamps were obliterated with a special postmark produced by Aerotarg, in black or dark red, depicting the arms and the name of the town, date and time. Postmarks in other colours are forgeries. 

Aerotarg stamps with Lodz and Krakow postmarks were cancelled to favour, using an genuine obliterator prepared for use by Aerotarg, but were never flown.

The total printing was 50,000 of each value but very few of these were used genuinely, most of the printing was remaindered. Genuine flown covers will have normal postage stamps in addition to the Aerotarg stamps. The remainders were sold mint or on unaddressed covers with the two Aerotarg stamps and genuine Aerotarg cancels but they did not have any normal Polish stamps on them.