Six Irish cities will have zero emission postal deliveries by the end of the year.
Dublin has become the first capital city in the world to have a postal service with no carbon being released into the atmosphere.
The semi-state body has invested €7.5m into its fleet of 47 electric vans and trucks.
Nationwide there are 212 e-vehicles with 900 expected in the next two years.
Oisin Coughlan, Director of Friends of the Earth, said their ability to use bicycles has helped reach the target.
"Postal delivery is a mix of technologies and obviously the bit that we see has always been low carbon, it's postmen and women on bicycles and their feet," he said.
"To see the vans and trucks replaced by electric vans and trucks is fantastic."
An Post intends to have the initiative rolled out to Galway, Cork, Kilkenny, Limerick and Waterford by the end of the year.
Mr Coughlan added rolling it out to rural areas may take time.
"Certainly more challenging; electric cars the range is growing but certainly makes sense to start in the capital city and then to go to the bigger cities and towns," he said.
"I could see that a lot of this will happen over the course of the next decade across Ireland. They have to make a start and they're making a big start here by doing it here in the city centre in Dublin."