You will be given a definition of a task first, then some input of the task.
In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

What is the most common way to transmit email?, Context: Many mailbox providers are also access providers, while others are not (e.g., Yahoo! Mail, Outlook.com, Gmail, AOL Mail, Po box). The definition given in RFC 6650 covers email hosting services, as well as the relevant department of companies, universities, organizations, groups, and individuals that manage their mail servers themselves. The task is typically accomplished by implementing Simple Mail Transfer Protocol (SMTP) and possibly providing access to messages through Internet Message Access Protocol (IMAP), the Post Office Protocol, Webmail, or a proprietary protocol.
Output:
(SMTP)