A Bit about Email

Email's architecture divides the sending and receiving process into distinct components—mail user agents (MUA), submission agents (MSA), mail transfer agents (MTA), local delivery agents (LDA), and message stores—designed in the 1980s when server reliability and bandwidth were severely limited. This separation allows MTAs to queue and retry failed deliveries (typically for five days) so that temporary outages don't bounce messages, while users can access stored emails asynchronously through their mail client. The system relies on SMTP protocol and DNS MX records to route messages between mail servers across different organizations.