It's when sending mail from one system to another that things get complicated. The main way the Lab keeps the communication channels open is with a common language, or more precisely, a standard set of mail protocols that different systems can understand. SMTP was developed 25 years ago for mail transfer over the Internet, where it is still used. This makes communication in some ways easier for the UNIX systems at the Lab, since they use SMTP to begin with. The translators are known as gateways.
Mail have similar gateways.
This allows message transfer to be flexible. Typically, if a message can't be delivered after three days, it is returned to the sender along with an explanation. Each user registered at the EPO has an alias consisting of a first and middle initial, and last name. The alias is indexed with the e-mail address specific to a particular system where the user prefers to receive mail. The EPO also serves as a resource standard.