What is Port 993?

by Colin Cohen | Published on November 13, 2023

Port 993 is dedicated to the Internet Message Access Protocol (IMAP). This allows multiple email clients to download mail from an email server over the port using SSL/TLS encryption and remain in sync.

Port 993 Explained

You use port 993 to securely download email from an email server using IMAP. All major email clients, such as Gmail and Outlook, support IMAP to communicate with email servers over the port. This communication includes authenticating the user and retrieving new mail messages.

Does the IMAP 993 Port Use TCP or UDP?

You use the TCP transport protocol when using IMAP over port 993. This is because TCP, unlike UDP, provides reliable transfer of commands, responses, and message data.

Is Server Port 993 Encrypted?

Yes, when you use IMAP over port 993, you must use SSL/TLS encryption between the clients and the server. This means that both the server and the clients must implement SSL/TLS. If you want to use IMAP without encryption, you should use port 143.

What is IMAP?

IMAP is a protocol for downloading mail messages from an email server to an email client. The protocol doesn’t delete messages from the server after it retrieves them, allowing multiple email clients to stay in sync.

IMAP Explained

IMAP is a protocol that lets email clients download messages from an email server. Unlike POP3, which is an older protocol that can also download mail messages, IMAP allows syncing of multiple email clients. It also has the following additional features:

  • Delivers fast response times by staying connected to the server for long periods

  • Provides message state information (whether a message has been read, replied to, or deleted)

  • Can maintain multiple mailboxes

  • Can perform server searches

  • Enables server push notifications 

IMAP uses port 143 for unencrypted communication and port 993 for encrypted communication.

Message Retrieval and IMAP

In today’s world, people often have multiple devices, each with its own email client. These clients must stay in sync so the same messages exist across a person’s computer, phone, and tablet. IMAP accomplishes this by not deleting messages from the server after they retrieve them. This way, each client can maintain the same set of messages.

Are There Other Protocols on Port 993 Besides IMAP?

When using port 993 to download mail using the IMAP protocol, you use other protocols as well. You use the TCP transport protocol to handle communication between the clients and server, and you use SSL/TLS protocols to handle encryption between the devices.

What is IMAP 993 Used For?

When a user wants to receive new mail messages, the email clients on their device(s) contact the appropriate email server using IMAP, which then delivers the messages. This is done over port 993 for encrypted communication and port 143 for unencrypted communication.

Why Does IMAP Need a Default Port?

Every Internet protocol has a default port, which the protocol uses unless you choose a nonstandard port. The protocol uses these ports to facilitate communication between two devices. IMAP has two default ports: 143 and 993.

Difference Between Port 993 and Port 143

Port 993 and port 143 are both default IMAP ports. You use port 993 for encrypted communication and port 143 for unencrypted communication. Both the email clients and the email server must use the same port.

Email Clients and How They Communicate With Port 993 IMAP

Email clients communicate with email servers over port 993 to download mail messages using IMAP. They do this by sending commands to the server within an IMAP session. A typical session can include the following steps:

  • Connection establishment

  • User authentication

  • Mailbox selection

  • Message fetching

  • Message attribute storing

  • Connection termination

What are the Types of Devices That Use Port 993?

Two types of devices use IMAP over port 993. Client devices, including computers, phones, and tablets, allow users to download new mail messages from email services. Server devices deliver the messages to the clients over the port.

IMAP 993 Port Vulnerabilities

By using IMAP over port 993, you are requiring the use of encrypted communication. This eliminates many vulnerabilities associated with using the protocol over port 143. But you still must properly configure IMAP and SSL/TLS to avoid other types of vulnerabilities.

IMAP Protocol Misconfigurations

IMAP implementations can be susceptible to vulnerabilities even on port 993 if you do not properly configure your email servers. You should apply organizational security policies to your configurations, particularly those related to authentication and message management. Without this, you can expose your organization to vulnerabilities such as password spraying.

How to Implement SSL/TLS Properly

SSL/TLS allows you to encrypt communication during IMAP sessions. However, using older SSL/TLS protocols such as TLS 1.0 or TLS 1.1 can lead to a wide range of vulnerabilities. This includes POODLE, BEAST, Heartbleed, and CRIME. You should always use the latest protocol version, which is currently TLS 1.3.

Potential Port Conflicts with 993 IMAP

Conflicts can occur if you attempt to run multiple services over port 993. To resolve this, you can either stop the conflicting service or configure one of the services to use another port.

Can Multiple Services Interrupt Port 993?

Like all TCP ports, only one service can use port 993 at one time. If you are experiencing a conflict on the port, you must stop the existing service before starting the IMAP service.

Can You Run Multiple IMAP Services Simultaneously?

You cannot run multiple IMAP services simultaneously on the same port. However, you can run multiple IMAP services simultaneously over different ports. To do this, you must configure both your email server and all email clients that connect to it so that it uses a port other than 993.


Modern email clients use IMAP over port 993 to download email messages from email servers using a secure connection. By using IMAP, you can sync multiple devices with the same account. It does this by not deleting the messages on the server after it downloads them.

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