SMTP
Definition
Simple Mail Transfer Protocol - the standard method computers use to send emails across the internet, ensuring reliable email delivery.
Use Cases
- Amazon: Sending order confirmations, shipping notifications, and account alerts to customers — Amazon uses email infrastructure that relies on standard email protocols (including SMTP for message transfer between mail systems) along with authentication standards like SPF/DKIM to improve deliverability. (Reliable delivery of high-volume transactional emails that support customer communication at scale)
- Google: Helping organizations route outbound mail from on-premises apps and devices through Google Workspace — Organizations configure the Gmail SMTP relay service to accept mail from approved IPs or authenticated users, then relay messages to the internet using SMTP with policy controls and logging. (Centralized outbound email routing with improved control, auditing, and deliverability for business domains)
Provider Equivalents
- AWS: Amazon Simple Email Service (Amazon SES)
- Azure: Azure Communication Services - Email
- GCP: Gmail SMTP relay service
- OCI: OCI Email Delivery
Frequently Asked Questions
- What's the difference between SMTP and IMAP?
- SMTP is used to send email (from your app or mail server to another mail server). IMAP is used to read and sync email from a mailbox (your email client pulls messages from the server and keeps folders in sync). In practice: SMTP = sending, IMAP = receiving/syncing.
- When should I use SMTP?
- Use SMTP when you need to send emails from an application or system—such as password resets, invoices, alerts, or contact-form messages. In cloud environments, you typically use a managed email service (like Amazon SES or OCI Email Delivery) and connect via SMTP credentials or an API for better deliverability and rate limits.
- How much does SMTP cost?
- SMTP itself is a free protocol, but sending email has costs depending on what you use: (1) a managed email provider charges per email sent and sometimes per data volume, (2) your compute/network costs if you run your own mail server, and (3) optional add-ons like dedicated IPs, deliverability tools, or higher sending limits. Pricing varies by provider and volume.
Category: networking
Difficulty: intermediate
Related Terms
See Also