What is SMTP Server? A Simple Email Sending Guide

Key takeaways 

• SMTP (Simple Mail Transfer Protocol) serves as the backbone for sending emails across the Internet. 
• SMTP differs from receiving protocols like POP3 and IMAP – you need SMTP to send emails while POP3/IMAP handle retrieving emails from servers. 
• Using secure SMTP configurations with TLS/SSL encryption and proper authentication helps protect your email communications from interception. 
• Most email platforms use standard SMTP ports (25, 465, 587), but your specific configuration depends on your service provider’s requirements. 
• Common SMTP issues like failed deliveries often stem from authentication problems, incorrect port settings or server connectivity issues. 

Introduction

Every time you hit “send,” your email takes a rapid, invisible journey across servers, networks and data centers. Within seconds, it lands in your recipient’s inbox. Billions of emails depend on this behind-the-scenes system called SMTP. 

But what is SMTP and how does it make this possible? 

SMTP, or Simple Mail Transfer Protocol, has quietly powered global email since 1982. This protocol follows a specific set of rules to ensure emails consistently reach their intended destinations. Without SMTP, emails would have no reliable way to travel across the internet. 

This guide explains exactly how SMTP works. You’ll also learn how to configure your email settings, troubleshoot common issues and ensure messages always reach recipients. 

Let’s get started. 

What is SMTP server in email? 

SMTP (Simple Mail Transfer Protocol) is a technical standard used for sending emails over the Internet. It controls how your outgoing email moves from your device to your recipient’s inbox. When you select “send” in your email client, SMTP takes over the delivery process. 

Think of SMTP as the postal service of digital communication. Your email message begins its journey when your mail client contacts an SMTP server. This server then determines how to route your message to the recipient’s mail server. Finally, the message arrives in the recipient’s inbox. 

Basic role of SMTP in emails 

SMTP performs several essential functions in the email delivery process: 

1. It establishes a connection between your device and the outgoing mail server. 
2. It verifies the sender and recipient email addresses. 
3. It transfers your message to the appropriate recipient’s SMTP server. 
4. It handles any delivery status notifications if problems occur. 

Unlike other protocols that retrieve messages, SMTP focuses exclusively on sending. You need separate protocols like POP3 or IMAP to receive emails. This division of responsibilities keeps email systems organized and efficient. 

Also read: POP3 vs. IMAP: Understanding the Differences in Email Hosting Protocols 

Your email service provider maintains SMTP servers that handle millions of transmissions daily. These servers follow strict rules to ensure messages reach their destinations securely. Without this standardized approach, reliable email communication would be impossible. 

What are the key components of an SMTP server?  

An SMTP server contains several essential components that work together to process your emails. Understanding these elements helps you configure email systems properly and troubleshoot delivery problems effectively.  

1. Mail transfer agents 

Mail transfer agents (MTAs) form the core of any SMTP system. These specialized programs handle the actual transmission of emails between servers. Popular MTA software includes Postfix, Sendmail and Microsoft Exchange.  

MTAs perform several critical functions:  

1. They accept messages from mail clients and other MTAs. 
2. They determine the best route to the recipient’s server. 
3. They queue messages when immediate delivery isn’t possible. 
4. They retry failed deliveries based on configured schedules. 
5. They generate delivery status notifications for failed messages. 

Your MTA also applies security rules to prevent spam and protect your system. It verifies sending permissions, checks authentication credentials and enforces rate limits. These protections maintain your server’s reputation and prevent abuse.  

Modern MTAs contain sophisticated routing capabilities. When your email travels across the internet, it might pass through several intermediary MTAs before reaching its destination. Each transfer adds routing information to the message header.  

Now, let’s look at the commands used in the process to better understand what is SMTP and how it functions. 

2. SMTP commands and responses  

SMTP relies on a simple text-based command system. Your email client sends specific commands to the server, and the server responds with standardized codes. This conversation follows a predictable sequence during message transmission.  

Command	Description	Example
HELO/EHLO	Identifies the client to the server	EHLO mydomain.com
MAIL FROM	Specifies the sender’s address	MAIL FROM: sender@[example].com
RCPT TO	Specifies the recipient’s address	RCPT TO: recipient@]example].com
DATA	Indicates message content follows	DATA
QUIT	Ends the SMTP session	QUIT

The server responds to each command with numeric codes. Response codes beginning with 2 (like 250) indicate success. Codes starting with 4 indicate temporary failures, while codes starting with 5 indicate permanent failures.  

Understanding these commands helps when troubleshooting email problems. Most issues produce specific error codes that point to the underlying cause. For example, code 550 typically means the recipient address doesn’t exist or isn’t accepting mail.  

3. SMTP ports and security considerations  

SMTP ports determine how your email client connects to the server. Different ports support different security levels. Choosing the correct port affects both connectivity and protection.  

Port	Security	Common Use
25	Unencrypted	Standard SMTP (often blocked by ISPs)
465	SSL/TLS	Secure SMTP (implicit encryption)
587	STARTTLS	Modern secure SMTP (opportunistic encryption)
2525	Varies	Alternative when other ports are blocked

Modern email systems should use encrypted connections. Transport Layer Security (TLS) or Secure Sockets Layer (SSL) protect your messages during transmission. Without encryption, your emails travel as plain text that anyone could intercept and read.  

Port 587 with STARTTLS represents the current standard for secure email submission. This configuration provides strong protection while maintaining compatibility with most systems. Your email service provider should document their recommended port settings.  

Many ISPs now block port 25 to prevent spam. If you encounter connection problems, try alternative ports like 587 or 2525. Always configure your email client to require encryption for maximum security.  

Also read: How to Reduce or Eliminate Spam Emails Using a Spam Filter 

What is the difference between SMTP and other email protocols?  

Email relies on multiple protocols working together to provide complete functionality. While SMTP handles sending emails, other protocols manage receiving and storing messages. Understanding these differences helps you configure your email account correctly.  

1. SMTP vs POP3

What is SMTP compared to POP3? The key distinction lies in their functions. SMTP sends outgoing mail, while POP3 retrieves messages from your mail server to your local device.  

Feature	SMTP	POP3
Primary Function	Sends outgoing mail	Downloads incoming mail
Direction	Client to server	Server to client
Default Port	25, 587, 465	110, 995 (secure)
Message Storage	Delivers to server	Typically removes from server after download
Multiple Device Support	N/A	Limited (messages download to one device)

When you use POP3, your email client connects to the incoming server and downloads messages to your device. After download, the messages typically get removed from the server. This approach saves server storage space but limits access to a single device.  

POP3 works well for users who:  

• Access email from only one device  
• Have limited server storage  
• Need offline access to older messages  
• Don’t need to sync message status across devices  

Your email setup requires both protocols for complete functionality. SMTP handles your outgoing email, while POP3 manages retrieval. Both must be configured correctly in your mail client.  

2. SMTP vs IMAP 

Internet Message Access Protocol (IMAP) offers a more modern approach to email retrieval than POP3. Like POP3, IMAP handles incoming mail while SMTP manages outgoing messages.  

Feature	SMTP	IMAP
Primary Function	Sends outgoing mail	Manages server-stored mail
Direction	Client to server	Two-way synchronization
Default Port	25, 587, 465	143, 993 (secure)
Message Storage	Delivers to server	Keeps on server
Multiple Device Support	N/A	Full (syncs across all devices)

IMAP maintains your messages on the server, creating a synchronized experience across all your devices. When you read a message on your phone, it shows as read on your computer too. This approach uses more server storage but provides greater flexibility.  

IMAP supports folder structures, flags and message states. These features remain consistent across all your devices, allowing sophisticated organization. You can create complex filing systems that work identically everywhere you check your mail.  

Most modern email service providers recommend IMAP for its multi-device capabilities. This protocol better suits today’s connected lifestyle where people frequently switch between computers, phones and tablets.  

When to use each protocol?

Your email needs determine which protocol works best for receiving messages. SMTP always handles sending, regardless of your receiving protocol choice.  

Protocol	Best for	When to choose
SMTP	Sending mail	Always required for outgoing mail
POP3	Single-device setups	Limited server storage, one primary device
IMAP	Multi-device users	Consistent experience across devices

You always need SMTP to send emails. Configure your SMTP address according to your provider’s instructions. Typically, this looks like “smtp.[yourdomain].com” or “smtp.[serviceprovider].com”.  

Choose POP3 if you primarily use one device and have limited server storage. This protocol works well for simple setups with minimal storage needs. Remember that POP3 typically removes messages from the server after download.  

Select IMAP if you regularly check email from multiple devices. This protocol provides the most consistent cross-device experience. IMAP requires more server storage but offers better organization and synchronization.  

Most modern users benefit from using SMTP for sending and IMAP for receiving. This combination supports today’s multi-device workflow while maintaining full message organization capabilities.  

How can you set up an SMTP server? 

Setting up an SMTP server requires careful planning and technical configuration. You have two main options: use a third-party SMTP service or configure your own SMTP server. Your choice depends on your technical expertise, budget and specific requirements. 

Choosing the right SMTP service provider 

Several factors should guide your selection of an SMTP service provider: 

Factor	What to look for	Why it matters
Reliability	Uptime guarantees, redundant systems	Ensures consistent email delivery
Deliverability	Anti-spam measures, IP reputation	Helps emails reach inboxes, not spam folders
Security	TLS encryption, SMTP authentication	Protects sensitive information
Sending Limits	Daily/monthly message caps	Matches your volume requirements
Price Structure	Per-message or subscription pricing	Affects overall cost

For small businesses and personal sites, your web hosting provider often includes SMTP services. Dedicated SMTP providers like SendGrid, Mailgun and SMTP.com specialize in high-volume email delivery. These services offer advanced features like delivery analytics, bounce handling and dedicated IP addresses. Consider these options for marketing campaigns or transactional emails. 

Free SMTP servers exist for low-volume senders. Services like Gmail allow limited sending through their SMTP servers. However, these free services typically restrict volume and lack business features. For professional use, paid services provide better reliability and support. 

Bluehost SMTP solutions for seamless email delivery 

You need reliable SMTP services for consistent email delivery. Bluehost, for example, offers complete email solutions with all hosting plans, including Professional Email and Google Workspace options.  

Our email solutions include:  

• Pre-configured SMTP servers optimized for deliverability 
• Multiple security options including TLS encryption  
• Simplified setup through your hosting control panel  
• Professional email addresses matching your domain name  
• Reliable support for email-related issues 

These integrated services eliminate the need to configure separate SMTP providers. Your email capabilities activate immediately when you set up your hosting account. 

Setting up SMTP email server with Bluehost 

Bluehost makes SMTP configuration straightforward with our integrated email solutions. Follow these steps to set up your SMTP email server address with Bluehost: 

1. Log in to your Bluehost control panel. 
2. Navigate to the Email & Office section and click on “Email Accounts.” 
3. Create a new email account or select an existing one. 
4. Note down the SMTP server settings (server name, port, encryption method). 
5. Configure your email client or application with the provided SMTP settings. 

Your Bluehost SMTP server address typically follows the format mail.[yourdomain].com. For secure connections, use port 587 with STARTTLS encryption or port 465 with SSL/TLS. Always enable SMTP authentication and use your full email address as the username. 

After configuring your email client, send a test message to verify proper setup. If you encounter problems, double-check your settings against Bluehost’s documentation.  

Common SMTP server configurations and ports 

When configuring your email client or application, use the following common SMTP server settings: 

Encryption	Port	Server name
None	25	Mail.[yourdomain].com
SSL/TLS	465	Smtp.[yourdomain].com
STARTTLS	587	Smtp.[yourdomain].com

Replace “[yourdomain].com” with your actual domain name. 

These settings cover the most common configurations for SMTP servers. By selecting the appropriate encryption method and port, you can ensure that your email communications are secure and compliant with industry standards. 

It’s important to note that while using unencrypted SMTP on port 25 is still possible, it’s not recommended due to security limitations. Whenever possible, opt for encrypted connections using SSL/TLS or STARTTLS to protect your email messages from interception or tampering. 

Also read: How To Configure an Email Application – Client Setup SSL/TLS Settings – POP & IMAP 

What are common SMTP issues and how can you fix them? 

Email problems often stem from SMTP configuration issues. Some common SMTP issues include: 

1. Emails not sending or receiving

If you’re experiencing problems sending or receiving emails, try the following: 

• Double-check your SMTP server settings (server name, port, encryption). 
• Ensure your email client or application is using the correct authentication method (usually SMTP-AUTH). 
• Check your sending limits and verify your account is in good standing. 

Incorrect SMTP server settings are a common cause of email sending issues. Verify that you’ve entered the correct server name, port and encryption method in your email client or application. Also, ensure that you’re using the proper authentication method, which is typically SMTP-AUTH. 

If you’re still having trouble, check your sending limits and account status with your SMTP service provider. Too many emails or a problem with your account can cause delays or blocks. 

2. Connection timeout troubleshooting 

If you encounter connection timeouts when trying to send emails: 

• Verify your internet connection is stable. 
• Check if your ISP or network is blocking the SMTP ports (25, 465, 587). 
• Try increasing the connection timeout setting in your email client or application. 

Connection timeouts can occur due to network issues, such as an unstable internet connection or blocked ports. Start by ensuring that your internet connection is stable and reliable. If the problem persists, contact your ISP or network administrator to verify that the SMTP ports (25, 465 and 587) are not being blocked. 

You can also try increasing the connection timeout setting in your email client or application. This setting determines how long the client will wait for a response from the SMTP server before timing out. Increasing this value can help compensate for slow or unstable network connections. 

3. Email deliverability problems 

To improve email deliverability and avoid issues like spam filtering or bounced messages: 

• Ensure your DNS records (SPF, DKIM, DMARC) are properly configured. 
• Maintain a clean email list and promptly remove invalid or bounced addresses. 
• Avoid using spammy words or phrases in your email content. 
• Monitor your sending reputation and bounce rates. 

Email deliverability issues can be caused by a variety of factors, including improper DNS configuration, poor email list hygiene and spam-like content. To minimize these issues, start by ensuring that your DNS records (SPF, DKIM and DMARC) are properly configured and a backup server is available. These records help receiving servers verify your identity and prevent email spoofing. 

Also read: Troubleshooting Email Deliverability Issues 

Finally, monitor your sending reputation and bounce rates to identify potential issues early. A high bounce rate or poor sending reputation can indicate underlying problems with your email practices, such as sending to invalid addresses or using spam-like content. 

What are some best practices for using SMTP securely? 

Secure email practices protect both you and your recipients. Implementing these best practices helps prevent data breaches and message interception while maintaining reliable delivery. 

1. Use authenticated SMTP (SMTP-AUTH) 

Enable and require authentication (SMTP-AUTH) for your SMTP server. This ensures only authorized users can send emails through your server, reducing the risk of spam or unauthorized access. 

Authenticated SMTP adds an extra layer of security by requiring users to provide valid credentials before sending emails. This helps prevent unauthorized individuals from using your SMTP server to send spam or malicious messages. 

2. Enable TLS or SSL encryption 

Use TLS (STARTTLS) or SSL/TLS encryption for your SMTP connections. Encryption protects the confidentiality and integrity of your email messages as they travel across the internet. 

When you enable encryption, the contents of your email messages are scrambled, making them unreadable to anyone who might intercept them. This is particularly important when sending sensitive information, such as financial data or personal details. 

3. Limit open relays to prevent spam 

An open relay allows anyone to send email through your server without authentication. Never configure an SMTP server as an open relay. This dangerous configuration allows anyone to send mail through your server without authentication. Spammers actively search for open relays to abuse for sending spam while hiding their identity. 

Implement authentication requirements for all mail relay operations. Configure your server to require valid credentials before accepting outgoing mail. This practice ensures only authorized users can send through your system. 

Final thoughts 

SMTP remains the internet’s standard protocol for sending email, enabling billions of messages to travel reliably each day. Its simple yet effective design has stood the test of time since 1982. 

Most users will find the SMTP services provided by their hosting company or email provider sufficient for daily needs. Those with specialized requirements might prefer dedicated SMTP services for additional features and reliability. 

The best practices outlined in this guide help you avoid common email delivery problems and maintain consistent communication with your recipients. 

Ready to set up reliable email for your domain? Bluehost offers secure SMTP services with all hosting plans, making email configuration straightforward.  

Get started with Bluehost email hosting today and enjoy professional, reliable email delivery for your personal or business communications. 

FAQs