IMAP & SMTP: Role and key differences (2025)

You hit "send" on an email, and it’s delivered in seconds. Later, you check your inbox on your laptop, and even on your tablet—only to find everything perfectly synced, as if by magic. That seamless experience isn’t magic at all. It’s made possible by email protocols like IMAP and SMTP.

Now, here’s the thing: While they’re often mentioned together, IMAP vs. SMTP isn’t about choosing one over the other. They play completely different roles, and both are essential for email to work the way we expect.

Let’s break it down in simple terms.

What is IMAP?

IMAP (Internet Message Access Protocol) is a protocol that allows you to access emails directly from the mail server. Instead of downloading and storing your emails on one device, IMAP helps you keep everything on the server, just like how we store images on the cloud and access them across devices.

With IMAP, you can open the same inbox from your phone, tablet, or laptop and see the same emails. When you delete or move an email in one place, the change reflects everywhere.

What is SMTP?

SMTP (Simple Mail Transfer Protocol) is a protocol that pushes your emails from your email client (Zoho Mail, Gmail, Outlook, or an app's backend system) to the recipient's mail server. Without the help of SMTP, your emails would never actually leave your outbox.

With SMTP,  you can authenticate your emails to ensure that they're accepted by the recipient's server and are delivered safely—just like a food delivery person who delivers food from the restaurant to the person who placed the order.

What are the key differences between IMAP and SMTP?

If IMAP is about receiving and organizing emails, SMTP is about sending them out into the world.
 

IMAP and SMTP: How do they work together?

1. When you compose and send an email, SMTP pushes it to the recipient’s email server.

2. Once delivered, the recipient’s mail client uses IMAP to fetch and display it.

3. If IMAP is used, the email stays synced across all devices.

IMAP or SMTP?

You cannot choose between IMAP and SMTP. With emails, it isn’t really about picking between SMTP and IMAP because they’re designed to complement each other.

Today’s email systems typically use SMTP for sending and IMAP for retrieving and syncing because:

• We expect our emails to stay in sync across all devices.

• IMAP stores messages on the server, making them safe even if a device is lost.

• SMTP ensures that emails actually leave your outbox and get to the right destination.

In short, SMTP delivers. IMAP syncs and organizes. And together, they make email communication seamless. 

What is the role of IMAP and SMTP in transactional email sending and delivery?

SMTP  

• Ensures that your transactional email is delivered.

• When your app or system sends a transactional email (like a password reset, OTPs, shipping update, or invoice), it uses SMTP to push the email out from your server to the recipient’s mail server.

• Without SMTP, the message would never leave your outbox.

IMAP 

• Ensures that your transactional email stays synced.

• Once that transactional email is sent and stored, users may need to view it across multiple devices, like their phone, laptop, or desktop.

• IMAP keeps the inbox updated everywhere. If the recipient opens the order confirmation on their phone and later checks on their laptop, it’ll appear exactly the same.

Why should you choose a reliable SMTP transactional email service?

Choosing the right SMTP service is crucial because it directly impacts whether your emails reach inboxes or get lost in spam folders. A reliable SMTP service should offer:

• High deliverability: Ensure your emails consistently reach the inbox, not the spam folder.

• Scalability: The ability to handle both low and high email volumes without performance issues during peak business hours or seasonal spikes.

• Security: Features like authentication, encryption, and compliance with email standards to safeguard your communication.

• Reputation management: Proper handling of bounces, blacklists, and domain authentication safeguards your sending reputation.

• Tracking and insights: Tracking opens, clicks, bounces, and delivery reports in real-time to measure performance.

• Strong customer support: Assistance when you face technical or deliverability challenges.

• Affordable pricing: Choose a platform that provides all the above and also has a transparent pricing without any hidden costs.

Evaluating these factors helps you identify an SMTP provider you can depend on for your business communication. 

Why should you try Zoho ZeptoMail as your SMTP service?

ZeptoMail is built to address the specific needs of transactional email delivery, making it a reliable choice for businesses. Here’s why it stands out:

Separate infrastructure

ZeptoMail has a separate infrastructure for transactional email sending and prevents deliverability issues caused by mixing of promotional emails with transactional emails.

Reliability

Transactional emails like password resets, OTPs, and order confirmations are time-sensitive ones. ZeptoMail ensures high uptime and consistent performance, so your critical emails are delivered without delays or interruptions.

Security

Your business data and your customers’ confidential details deserve the highest level of protection. ZeptoMail provides multiple layers of security including encryption, authentication (DKIM, DMARC), and strict data security measures to keep every email safe.

Compliance

ZeptoMail is GDPR-compliant and adheres to global standards, helping your business meet regulatory requirements with ease. No matter your industry or region, ZeptoMail is built to support compliance needs.

Ease of integration

ZeptoMail makes it simple to get started. Whether you prefer SMTP relay or API-based sending, it supports both. With code libraries available in popular programming languages, you can connect it to your website or application quickly without the hassle of complex setups.

Scalability

As your business grows, so does your email volume. ZeptoMail is designed to scale effortlessly, whether you’re sending thousands of transactional emails a day or handling peak traffic during high-demand events like Black Friday.

Features and customization

Every business has unique email needs. ZeptoMail provides detailed email tracking (opens, clicks, bounces), custom reports, and flexible options for managing lists, ensuring you can adapt the platform to suit your requirements.

Support

Backed by Zoho’s trusted ecosystem, ZeptoMail comes with responsive customer support and extensive documentation. This ensures smooth implementation and quick resolution of any issues that arise.

Pricing

When it comes to pricing, ZeptoMail keeps things simple. Instead of complicated tiers, hidden charges and costly add-ons, it runs on a credit-based system. You only pay for what you use, making enterprise-grade email delivery affordable for businesses of all sizes. For just 1 credit, you can send up to 10,000 transactional emails (valid for 6 months) from an account.

Key takeaways

Remember that IMAP and SMTP complement each other. Together, they guarantee that your transactional emails not only reach the recipient but also remain organized and accessible no matter where or how they’re opened.

• SMTP is for sending and delivering transactional emails.

• IMAP is for receiving, syncing, and managing those emails across devices.

• Always configure IMAP + SMTP together for full functionality.

• For businesses, use a trusted transactional email service like Zoho ZeptoMail with strong SMTP support to avoid delivery failures.

• Secure your email flow with SSL/TLS so that sensitive information stays protected.