1.
What is SMTP?
Emails, an indispensable part of working life, constitute a significant portion of both internal and external written communication. It is possible to find the technical details of this technology, which forms the most critical link in the series of protocols regulating communication between sender and receiver servers, in this article titled what is SMTP. By continuing to read, you can master the working principle of this protocol used to transmit emails in cloud-based systems and all other details.
SMTP stands for "Simple Mail Transfer Protocol," and this protocol is used to transmit emails over the internet. In other words, SMTP is involved in the process on the receiver and sender sides of an email sending operation. When the sending process is initiated; the Source Server performs a "Handshake" with the Destination Server and starts the transfer of data packets. In summary, SMTP is responsible for the secure and complete transmission of the email between servers, not for its display by the end-user. Therefore, SMTP works in conjunction with other protocols like POP3 and IMAP to allow the recipient to access and properly read the message. In addition to all these, this mail protocol forms the basis not only for personal email transmission today but also for automated email processes such as contact forms, membership confirmation emails, password reset notifications, and system alerts. Thus, it would be correct to say that SMTP is one of the critical components of modern digital communication.
2.
SMTP Components
The basic SMTP components that make up the email architecture and work integrated with the SMTP protocol are as follows:
- MUA (Mail User Agent): MUA is the client software that the end-user interacts with to compose and read emails (Outlook, Thunderbird, Webmail, etc.). Applications like Gmail, Outlook, or Thunderbird are examples of MUAs. The user writes, reads, and sends the email through these tools. When the sending process is initiated, the MUA hands the message over to the MSA to forward it to the next stage.
- MSA (Mail Submission Agent): MSA is the component that accepts the email coming from the user and checks if it is suitable for sending. Authentication, spam prevention, and format checks are performed at this stage. Especially in system emails sent via websites and applications, the MSA serves as a critical security layer.
- MTA (Mail Transfer Agent): MTA is the main component responsible for the routing and transmission of the email between servers. It moves the message from one server to another using the "Relay" method. This is the stage where the SMTP protocol is most actively used. Also, it should not be forgotten that an email may pass through multiple MTAs until it reaches the recipient.
- MDA (Mail Delivery Agent): MDA is the final stop of the email on the recipient side. At this stop, the message coming from the MTA is received and placed in the recipient's mailbox. After this process is completed, the user can access their email via protocols such as POP3 or IMAP. In other words, the MDA is the final component ensuring the delivery is completed smoothly.
3.
How Does SMTP Work?
When the components of SMTP complete their tasks among themselves, the protocol's working mechanism is considered to have operated smoothly. The process begins with the user issuing the "Send" command via the MUA. The email packet is transmitted to the Outgoing Mail Server via a TCP/IP connection. Here, SMTP Authentication is performed, and it is checked whether the sender is authorized. After checks are completed, the message is routed between mail servers on the internet and reaches the recipient's mail server. When the receiving server accepts the message, the email is delivered to the user's mailbox, its final destination, and becomes readable. It is possible to see this entire process step by step in the list below.
- The user sends the email via the email application or web interface.
- The message is transmitted to the mail server for sending authorization and security checks.
- The email is routed between mail servers on the internet.
- The message is accepted by the recipient's mail server.
- The email is delivered to the recipient's mailbox.
Difference of SMTP from POP3 and IMAP
We know that email communication is a whole of protocols working at different layers such as SMTP, POP3, and IMAP. POP3 and IMAP are the most heard among these protocols. So, what is the difference between SMTP and these? It is possible to see how SMTP differs from POP3 and IMAP in terms of scope by examining the table below.
| Protocol |
Primary Function |
When is it Used? |
| SMTP |
Enables sending of emails and transmission between servers. |
The moment an email is sent |
| POP3 |
Downloads emails from the server and moves them to the device. |
When the user wants to read their emails |
| IMAP |
Manages emails on the server in a synchronized manner. |
When email is accessed from multiple devices |
4.
Which Ports Does SMTP Use?
So, which ports does SMTP use? The SMTP protocol uses different communication ports depending on server configuration and encryption standards (SSL/TLS). While most systems today prefer ports offering encrypted connections, some ports are used only for server-to-server communication. You can see which ports SMTP uses in the list below.
- Port 25 is generally standard for server-to-server (MTA to MTA) communication. However, it may be blocked for end-user access by individual internet service providers (ISPs) to prevent spam.
- Port 587 is accepted as the standard for modern email submission. It offers a secure and encrypted connection with the STARTTLS protocol.
- Port 465 is used for fully encrypted email submission running over SSL/TLS.
5.
Gmail SMTP Settings
Thanks to Gmail SMTP settings, contact forms, notification emails, and automated transmissions can be sent securely via the Gmail infrastructure. At this stage, it should not be forgotten that due to security policies, it is mandatory to create a special "App Password" instead of the standard password to establish an SMTP connection in Gmail accounts where 2-Step Verification (2FA) is active. Otherwise, you may encounter authentication errors during email sending.
- SMTP server: smtp.gmail.com
- Port: 587
- Encryption method: TLS
- Authentication: On
- Username: Gmail email address
- Password: Gmail account password or app password
6.
Modern Email Infrastructure: Cloud-Based SMTP
Today, email sending processes are managed through cloud-based infrastructures instead of traditional physical servers. Cloud-based SMTP services offer scalability, high availability, and advanced security in email transmission. Corporate applications can manage High Volume Traffic without experiencing bottlenecks thanks to managed cloud services; and monitor Deliverability rates and error logs from a centralized panel.
You might also be interested in our article titled What Does Server Mean?.
7.
Frequently Asked Questions
What is an SMTP error?
An SMTP error is the situation where an email is rejected or cannot be delivered by the mail server during the sending process.
How to fix an SMTP error?
An SMTP error can be resolved by correctly configuring server settings, port information, and authentication options.
How to find the SMTP server?
SMTP server information is located on the official support page or in the account settings of the email provider used.
What should the outgoing mail server (SMTP) port be?
The most common and recommended SMTP port for the outgoing mail server is 587.
What is SMTP error 550?
SMTP error 550 indicates that the email was rejected due to unauthorized sending, spam blocking, or a recipient address issue.
What does SMTP do?
SMTP is the protocol that enables the sending of emails and their transmission between servers.
What is an SMTP password?
An SMTP password is the account password or app password used for authentication during email sending.
