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Enable and configure POP3 on an Exchange server

  • Artykuł

By default, POP3 client connectivity isn't enabled in Exchange. To enable POP3 client connectivity, you need to perform the following steps:

  1. Start the POP3 services, and configure the services to start automatically:

    • Microsoft Exchange POP3: This is the Client Access (frontend) service that POP3 clients connect to.

    • Microsoft Exchange POP3 Backend: POP3 client connections from the Client Access service are proxied to the backend service on the server that holds the active copy of the user's mailbox. For more information, see Client Access protocol architecture.

  2. Configure the POP3 settings for external clients.

    By default, Exchange uses the following settings for internal POP3 connections:

    • POP3 server FQDN: <ServerFQDN>. For example, mailbox01.contoso.com.

    • TCP port and encryption method: 995 for always TLS encrypted connections, and 110 for unencrypted connections, or for opportunistic TLS (STARTTLS) that results in an encrypted connection after the initial plain text protocol handshake.

    To allow external POP3 clients to connect to mailboxes, you need to configure the POP3 server FQDN, TCP port, and encryption method for external connections. This step causes the external POP3 settings to be displayed in Outlook on the web (formerly known as Outlook Web App) at Settings > Options > Mail > Accounts > POP and IMAP.

    POP settings in Outlook on the web.

  3. Restart the POP3 services to save the changes.

  4. Configure the authenticated SMTP settings for internal and external clients. For more information, see Configure authenticated SMTP settings for POP3 and IMAP4 clients in Exchange Server.

For more information about POP3, see POP3 and IMAP4 in Exchange Server.

What do you need to know before you begin?

  • Estimated time to complete each procedure: 5 minutes.

  • Secure Sockets Layer (SSL) is being replaced by Transport Layer Security (TLS) as the protocol that's used to encrypt data sent between computer systems. They're so closely related that the terms "SSL" and "TLS" (without versions) are often used interchangeably. Because of this similarity, references to "SSL" in Exchange topics, the Exchange admin center, and the Exchange Management Shell have often been used to encompass both the SSL and TLS protocols. Typically, "SSL" refers to the actual SSL protocol only when a version is also provided (for example, SSL 3.0). To find out why you should disable the SSL protocol and switch to TLS, check out Protecting you against the SSL 3.0 vulnerability.

  • To learn how to open the Exchange Management Shell in your on-premises Exchange organization, see Open the Exchange Management Shell.

  • You need to be assigned permissions before you can perform this procedure or procedures. To see what permissions you need, see the "POP3 and IMAP4 Permissions" section in the Clients and mobile devices permissions topic.

  • For information about keyboard shortcuts that may apply to the procedures in this topic, see Keyboard shortcuts in the Exchange admin center.

Tip

Having problems? Ask for help in the Exchange forums. Visit the forums at: Exchange Server, Exchange Online, or Exchange Online Protection.

Step 1: Start the POP3 services, and configure the services to start automatically

You can perform this step by using the Windows Services console, or the Exchange Management Shell.

Use the Windows Services console to start the POP3 services, and configure the services to start automatically

  1. On the Exchange server, open the Windows Services console. For example:

    • Run the command services.msc from the Run dialog, a Command Prompt window, or the Exchange Management Shell.

    • Open Server Manager, and then click Tools > Services.

  2. In the list of services, select Microsoft Exchange POP3, and then click Action > Properties.

  3. The Microsoft Exchange POP3 Properties window opens. On the General tab, configure the following settings:

    • Startup type: Select Automatic.

    • Service status: Click Start.

    When you're finished, click OK.

  4. In the list of services, select Microsoft Exchange POP3 Backend, and then click Action > Properties.

  5. The Microsoft Exchange POP3 Backend Properties window opens. On the General tab, configure the following settings:

    • Startup type: Select Automatic.

    • Service status: Click Start.

    When you're finished, click OK.

Use the Exchange Management Shell to start the POP3 services, and configure the services to start automatically

  1. Run the following command to start the POP3 services:

    Start-Service MSExchangePOP3; Start-Service MSExchangePOP3BE

  2. Run the following command to configure the POP3 services to start automatically:

    Set-Service MSExchangePOP3 -StartupType Automatic; Set-Service MSExchangePOP3BE -StartupType Automatic

For more information about these cmdlets, see Start-Service and Set-Service.

How do you know this step worked?

To verify that you've successfully started the POP3 services, use either of the following procedures:

  • On the Exchange server, open Windows Task Manager. On the Services tab, verify that the Status value for the MSExchangePOP3 and MSExchangePOP3BE services is Running.

  • In the Exchange Management Shell, run the following command to verify that the POP3 services are running:

    Get-Service MSExchangePOP3; Get-Service MSExchangePOP3BE

Step 2: Use the Exchange Management Shell to configure the POP3 settings for external clients

To configure the POP3 settings for external clients, use the following syntax:

Set-PopSettings -ExternalConnectionSettings "<FQDN1>:<TCPPort1>:<SSL | TLS | blank>", "<FQDN2>:<TCPPort2>:<SSL | TLS | blank>"...  -X509CertificateName <FQDN> [-SSLBindings "<IPv4Orv6Address1>:<TCPPort1>","<IPv4Orv6Address2>:<TCPPort2>"...] [-UnencryptedOrTLSBindings "<IPv4Orv6Address1>:<TCPPort1>","<IPv4Orv6Address2>:<TCPPort2>"...]

This example allows to configure the following settings for external POP3 connections:

  • POP3 server FQDN: mail.contoso.com

  • TCP port: 995 for always TLS encrypted connections, and 110 for unencrypted connections or opportunistic TLS (STARTTLS) encrypted connections.

  • Internal Exchange server IP address and TCP port for always TLS encrypted connections: All available IPv4 and IPv6 addresses on the server on port 995 (we aren't using the SSLBindings parameter, and the default value is [::]:995,0.0.0.0:995).

  • Internal Exchange server IP address and TCP port for unencrypted or opportunistic TLS (STARTTLS) encrypted connections: All available IPv4 and IPv6 addresses on the server on port 110 (we aren't using the UnencryptedOrTLSBindings parameter, and the default value is [::]:110,0.0.0.0:110).

  • FQDN used for encryption: mail.contoso.com. This value identifies the certificate that matches or contains the POP3 server FQDN.

Set-PopSettings -ExternalConnectionSettings "mail.contoso.com:995:SSL","mail.contoso.com:110:TLS" -X509CertificateName mail.contoso.com

Notes:

  • For detailed syntax and parameter information, see Set-PopSettings.

  • The external POP3 server FQDN that you configure needs to have a corresponding record in your public DNS, and the TCP port (110 or 995) needs to be allowed through your firewall to the Exchange server.

  • The combination of encryption methods and TCP ports that you use for the ExternalConnectionSettings parameter need to match the corresponding TCP ports and encryption methods that you use for the SSLBindings or UnencryptedOrTLSBindings parameters.

  • Although you can use a separate certificate for POP3, we recommend that you use the same certificate as the other Exchange IIS (HTTP) services, which is likely a wildcard certificate or a subject alternative name (SAN) certificate from a commercial certification authority that's automatically trusted by all clients. For more information, see Certificate requirements for Exchange services.

  • If you use a single subject certificate, or a SAN certificate, you also need to assign the certificate to the Exchange POP service. You don't need to assign a wildcard certificate to the Exchange POP service. For more information, see Assign certificates to Exchange Server services.

How you do know this step worked?

To verify that you've successfully configured the POP3 settings for external clients, run the following command in the Exchange Management Shell and verify the settings:

Get-PopSettings | Format-List *ConnectionSettings,*Bindings,X509CertificateName

For more information, see Get-POPSettings.

Step 3: Restart the POP3 services

After you enable and configure POP3, you need to restart the POP3 services on the server by using the Windows Services console, or the Exchange Management Shell.

Use the Windows Services console to restart the POP3 services

  1. On the Exchange server, open the Windows Services console.

  2. In the list of services, select Microsoft Exchange POP3, and then click Action > Restart.

  3. In the list of services, select Microsoft Exchange POP3 Backend, and then click Action > Restart.

Use the Exchange Management Shell to restart the POP3 services

Run the following command to restart the POP3 services.

Restart-Service MSExchangePOP3; Restart-Service MSExchangePOP3BE

For more information about this cmdlet, see Restart-Service.

To verify that you've successfully restarted the POP3 services, run the following command:

Get-Service MSExchangePOP3; Get-Service MSExchangePOP3BE

Step 4: Configure the authenticated SMTP settings for POP3 clients

Because POP3 isn't used to send email messages, you need to configure the authenticated SMTP settings that are used by internal and external POP3 clients. For more information, see POP3 and IMAP4 in Exchange Server.

How do you know this task worked?

To verify that you have enabled and configured POP3 on the Exchange server, perform the following procedures:

  1. Open a mailbox in Outlook on the web, and then click Settings > Options.

    Options menu location in Outlook on the web.

  2. Click Mail > Accounts > POP and IMAP and verify the correct POP3 settings are displayed.

    POP settings in Outlook on the web.

    Note: If you configured 995/SSL and 110/TLS values for the ExternalConnectionSettings parameter on the Set-PopSettings cmdlet, only the 995/SSL value is displayed in Outlook on the web. Also, if the external POP3 settings that you configured don't appear as expected in Outlook on the web after you restart the POP3 services, run the commands net stop w3svc /y and net start w3svc to restart Internet Information Services (IIS).

  3. You can test POP3 client connectivity to the Exchange server by using the following methods:

    • Internal clients: Use the Test-PopConnectivity cmdlet. For example, Test-PopConnectivity -ClientAccessServer <ServerName> -Lightmode -MailboxCredential (Get-Credential). For more information, see Test-PopConnectivity.

      Note: The Lightmode switch tells the command test POP3 logons to the server. To test sending (SMTP) and receiving (POP3) a message, you need to configure the authenticated SMTP settings as described in POP3 and IMAP4 in Exchange Server.

    • External clients: Use the POP Email test in the Microsoft Remote Connectivity Analyzer.

      Note: You can't use POP3 to connect to the Administrator mailbox. This limitation was intentionally included in Exchange 2016 and Exchange 2019 to enhance the security of the Administrator mailbox.

Next steps

To enabled or disable POP3 access to individual mailboxes, see Enable or disable POP3 or IMAP4 access to mailboxes in Exchange Server.