The E-0 was a pre-production bomber/reconnaissance version of Do 217E. It was powered by BMW 801A engines and armed with one forward firing 15 mm MG 151 cannon and five 7.92 mm MG 15 machine guns on gimbal mounts. It entered production and service in late 1940. Continued development led to the Do 217 E-1. The Do 217 E-1 first flew on 1 October 1940. Full production level bomber/reconnaissance variant, similar to the E-0, and followed it into production and service in late 1940, 94 were built. Additional armament consisted of a 20 mm cannon fitted in the nose. Its power plants were BMW 801s of 1,560 PS (1,539 horsepower (1,148 kW)). The aircraft could an internal bombload of 2,000 kg. Alternatively, it could carry a load of two LMW aerial mines or one torpedo. The E-2 could carry three mines.

In late 1940, testing under operational conditions began. By March 1941, 37 Do 217s had been built and test flown. Many of the E-1 variants, now being built in increasing numbers, were selected for conversion to the new improved fighter variants; the planned 217H, P and R series. A large number and these 'fighter/bomber' aircraft were put through severe testing runs between July and September 1941. Dornier was able to gain valuable knowledge for the future improvement of the armament and bomb jettisoning systems. Of the first six prototypes, two (the third and sixth) were delivered to operational units. The third, Wrk Nr. 1003 was lost on 22 May 1941 (at Rechlin) and 1006, the sixth prototype, was severely damaged on 11 April 1941 whilst with Kampfgeschwader 40.

Sources:
Gunston, Bill - The Encyclodepia of the Worlds Combat aircraft, 1976, Chartwell Books, Inc., New York
Brown, Eric, Captain - Wings of the Luftwaffe, 1979, Airlife Publishing Ltd., Shrewsbury
Gunston, Bill & Wood, Tony - Hitler's Luftwaffe, 1977, Salamander Books Ltd., London
Donald, David - The Complete Encyclopedia Of World Aircraft, 1997, Brown Packaging Books Ltd., London
Wikipedia - Dornier Do 217