SMTP is a protocol for sending and receiving emails across networks. ISPs provide mail server addresses, which require authentication for outbound mail. Webmail works similarly but is accessible from any computer. Emails are unencrypted and less private than physical mail, but encryption options are available.
The Simple Mail Transfer Protocol (SMTP) is a set of standardized rules or protocols for sending and receiving email across networks such as the Internet. A computer running SMTP is referred to as a mail server and ideally has near constant uptime. The SMTP mail server can both send and receive mail, although at the client level we associate SMTP with an outgoing mail server and Post Office Protocol 3 (POP3) with incoming mail.
Mail clients require an address for outgoing mail server and POP3 or incoming mail server to collect and send mail. Internet Service Providers (ISPs) provide these addresses to customers when they sign up for a subscription or contract, and mail server addresses are also commonly listed on ISPs’ websites. In some cases both outgoing and incoming mail will be handled by a single server, such as mail.(yourisp).com; but often the outgoing mail server address looks like smtp.(yourisp).com and the incoming address, pop3.(yourisp).com.
Authentication is required to access an outgoing mail server, consisting of the username and password associated with the customer’s ISP account. This protects the ISP from handling outbound email generated by non-customers, which could quickly bog down its resources. Additionally, authentication allows server administration to more easily monitor activity on their outgoing mail server to help prevent abuse such as spam and fraud.
Once mail is sent to an outgoing mail server, the associated SMTP server reads the email message headers to forward the message to its destination. Starts a dialog between itself and the next mail server along the way. The dialogue takes the form of a set of requests and responses, moving the mail forward to its final destination. Mail may travel through several intermediate hosts before reaching the host that acts as the recipient’s incoming mail server. If there is a problem en route, mail may be re-sent to retrace its path to the sender, arriving as undeliverable.
A web-based email service runs its own mail servers that work just like an ISP’s mail servers. The only difference is that clients access the website to read, write and send mail, rather than opening a personal email client from their desktop. Webmail such as Gmail® is very popular because it makes mail accessible from any computer with an Internet connection. It also prevents virus-laden mail from being downloaded to your personal hard drive, as the mail arrives at (and is read from) the website’s server.
It is important to note that e-mail must be considered public because it is sent unencrypted; a term used for plain text communications sent over a network that can be read by anyone. From the outgoing mail server to the many forwarding hosts and the final incoming mail server, email is less private than a postcard sent via standard mail and even more so with web-based services that rely on marketing. Only encrypted email is considered private, as it is hardcoded before being sent and is not encrypted by the recipient upon arrival. Popular email programs have the ability to use a third-party plug-in to provide built-in encryption, including Microsoft® and Mozilla® Thunderbird email clients.
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