The two primary methods for email delivery are distinguished by how messages arrive on a client device. One system involves the client device actively requesting new messages from the server at regular intervals. The other involves the server automatically sending new messages to the client device as soon as they arrive. An example of the former would be a desktop email client configured to check for new messages every 15 minutes, while the latter is exemplified by instant notifications on a smartphone when a new email arrives in the inbox.
The efficiency of email communication is significantly influenced by the delivery method employed. One approach can conserve battery life and network bandwidth when messages are infrequent, as the device remains inactive until its scheduled check. The alternative method offers near-instant delivery, ensuring timely access to critical information. Historically, the technology where clients request email dominated early email systems, reflecting the limitations of then-available networking and device capabilities. However, the desire for immediacy has driven the development and widespread adoption of methods where the server initiates delivery.