Protocol Roles in Email Communication
You may have noticed that SMTP is used for most of this communication process. In fact, if the recipient uses a machine that runs SMTP software, which is common for those using dial-up UNIX shell Internet access, the process of sending email uses SMTP exclusively. SMTP servers must, however, always be available on the Internet and ready to accept mail. Most people access the Internet using devices that aren't always online or that don't run SMTP software. That is why the last step, email access and retrieval, is usually required.
It might have been possible to define the email system so that this last step of communication was carried out using SMTP as well, which would mean the entire system used the same ...
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