SMTP (Simple Mail Transfer Protocol) — a protocol responsible for sending email. It transfers emails from the sender to the mail server and then — to the recipient’s server.
SMTP is used specifically for outgoing email. Receiving and synchronizing incoming emails work through other protocols — for example, IMAP or POP3.
Where SMTP is used
SMTP is used not only when sending regular emails. Many automated messages that users receive from websites and services are sent through it.
These may include:
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Registration: emails with a code or link to verify an email address.
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Service notifications: information about an order, payment, or changes to an account.
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Access recovery: emails with a password reset link.
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Email campaigns: promotional, informational, and other mass emails.
SMTP is responsible specifically for transferring the message. Whether the email lands in the «Inbox» or spam depends not only on the protocol itself, but also on the sender’s reputation, domain settings, email content, and anti-spam filters.
SMTP in traffic arbitrage
In traffic arbitrage, SMTP is most often used where work involves email campaigns and automated email sending. The email account is connected to special software that can automatically send emails without manually logging in to the email service.
Access to SMTP itself is not the only important factor here. Email services may set limits on the number of outgoing emails, temporarily restrict sending due to suspicious activity, or block messages with anti-spam filters.
Therefore, having SMTP access does not in itself mean that any number of emails can be sent from the mailbox without restrictions.
SMTP, IMAP, and POP3 — what is the difference
Simply put, the difference between the three protocols lies in their functions:
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SMTP: sends emails.
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IMAP: works with emails on the server and synchronizes email.
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POP3: downloads incoming emails from the server.
Therefore, SMTP does not replace IMAP or POP3. When working with a mailbox, they can be used together: SMTP — for outgoing emails, IMAP or POP3 — for incoming emails.
