Here you will find national Diplomacy associations as well as main sites for national hobby communities (which might not have formal associations). The Diplomatic Corps is marked as a "cool site" as this is currently the closest we get to an international Diplomacy association.
Links to local and regional clubs which offer face-to-face play on a regular basis. If no club is listed for your area or country, check if there is a national site or association under "Hobby Organizations".
These links offer software that help you adjudicate and manage e-mail games. Some programs also produce maps for ongoing games. There are also sites that offer maps and other resources for specific software.