IANA, the organization responsible for global IP address allocation and other tasks, is also responsible for registering port numbers for common Internet services, which includes SMTP. If you want to deliver something to that business, you can’t just address it to the business complex, you also need a way to make sure it gets to the right place inside the business complex. A port is the number of a specific business in that business complex. Here’s an analogy to make it a little more human-friendly:Īn IP address is the physical street address of a business complex. A port identifies a specific application/service running on that computer, like SMTP.Mail servers are much like website servers in that, while there might be a user-friendly front-facing domain name, the actual communication happens via IP addresses, like 222.501.285.45 (for more on how this happens, check out our introduction to the Domain Name System, or DNS).Ī “port” is another way to help computers ( like two mail servers) communicate with one another: Then, the outgoing mail server needs a way to transfer your email to the recipient’s incoming mail server. It’s what mail servers use to send and receive emails on the Internet.įor example, when you send an email, your email client needs a way to upload the email to the outgoing mail server. SMTP, short for Simple Mail Transfer Protocol, is the standard protocol for email transmission on the web.
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