What is SMTP?
Overview
Your ability to send and receive emails is largely due to 3 TCP protocols: SMTP, IMAP, and POP3.
SMTP
Start with SMTP because its primary function is different from the other two.
SMTP or Simple Mail Transfer Protocol is mostly used for sending out email from an email client (e.g. Microsoft Outlook, Thunderbird, or Apple Mail) to an email server.
It's also used for relaying or forwarding mail messages from one mail server to another.
The ability to relay messages from one server to another is necessary if the sender and recipient have different email service providers.
SMTP, which is specified in RFC 5321, uses port 25 by default.
It may also use port 587 and port 465.
The latter, which was introduced as the port of choice for secure SMTP (a.k.a. SMTPS), is supposed to be deprecated.
But in reality, it's still being used by some mail service providers.
Now that you have a basic understanding of SMTP.
Your ability to send and receive emails is largely due to 3 TCP protocols: SMTP, IMAP, and POP3.
SMTP
Start with SMTP because its primary function is different from the other two.
SMTP or Simple Mail Transfer Protocol is mostly used for sending out email from an email client (e.g. Microsoft Outlook, Thunderbird, or Apple Mail) to an email server.
It's also used for relaying or forwarding mail messages from one mail server to another.
The ability to relay messages from one server to another is necessary if the sender and recipient have different email service providers.
SMTP, which is specified in RFC 5321, uses port 25 by default.
It may also use port 587 and port 465.
The latter, which was introduced as the port of choice for secure SMTP (a.k.a. SMTPS), is supposed to be deprecated.
But in reality, it's still being used by some mail service providers.
Now that you have a basic understanding of SMTP.
Updated on: 21/06/2022
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