Log onto incoming mail server (POP3): Your e-mail server rejected your login

Question

Getting below error when configure POP3.

Log onto incoming mail server (POP3): Your e-mail server rejected your login. Verify your user name and password for this account in Account Settings. The server responded: -ERR Server Unavailable. 21

Client# Office 2021, Exchange# 2019

Change LoginType : SecureLogin", change it to Basic but no luck

Thanks,

Biplob

Answer 1

Hi @Md. Mahabubur Rahaman,

Welcome to Q&A!

To better understand your problem, please provide more information to us:

Was the login functionality working properly before?

When did this issue first occur?

How many users are affected by this issue?

Were there any related changes made prior to the issue appearing?

For your reference, the official document provides detailed steps on how to enable and configure POP3 on an Exchange server. You can access it here: Enable and configure POP3 on an Exchange server | Microsoft Learn. Please review the document and ensure that all steps have been correctly applied.If all settings are configured correctly, you could run the following command to check if POP3 is enabled for the affected account:

Get-CASMailbox -Identity user@example.com | Select-Object PopEnabled

If the value of PopEnabled is False, enable it by running this command:

Set-CASMailbox -Identity user@example.com -PopEnabled $true

Additionally, please share your POP3 configuration details with us by following these steps:

• Open the Outlook client.
• Click on File > Account Settings > Manage Profiles > Show Profiles.
• Add a new profile for POP3 by clicking Add.
• Select Manual setup or additional server types.
• Choose POP or IMAP.
• Fill in the required fields on the POP and IMAP Account Settings page.

• Take a screenshot of the POP and IMAP Account Settings page.
• Click More Settings and take screenshots of the following tabs:
  • General
  • Outgoing Server
  • Advanced
• Return to the POP and IMAP Account Settings page.
• Click Test Account Settings.
• Take a screenshot of any errors that appear during the test. Ensure that all screenshots have any private information (e.g., email addresses, server names, domain etc.) hidden before sharing.

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Answer 2

1. Verify POP3 is enabled on Exchange Server

• Check if POP3 services are running:
  • Open Exchange Management Shell
  • Run: Get-Service MSExchangePOP3*
  • Both "MSExchangePOP3" and "MSExchangePOP3BE" should show "Running"
• If not running:

  
       Start-Service MSExchangePOP3
  
       Start-Service MSExchangePOP3BE
  
       Set-Service MSExchangePOP3 -StartupType Automatic
  
       Set-Service MSExchangePOP3BE -StartupType Automatic
  
  

2. Check Authentication Settings

• In Exchange Admin Center:
  • Go to Servers → Protocols → POP3
  • Edit the POP3 settings and ensure:
    • Basic authentication is enabled
    • TLS or SSL is configured (usually port 995 for SSL)

3. Verify User Mailbox Settings

• Ensure POP3 is enabled for the user:

  
       Get-CASMailbox -Identity ******@domain.com | fl PopEnabled
  
  

• If disabled, enable it:

  
       Set-CASMailbox -Identity ******@domain.com -PopEnabled $true
  
  

4. Test Connectivity

• From the client machine, test basic connectivity:

  
       telnet mailserver.domain.com 995
  
  

  (If connection fails, check firewall/network settings)

5. Client Configuration

• In Outlook/Office 2021:
  • Server: mailserver.domain.com (or your Exchange server name)
  • Port: 995 (SSL) or 110 (non-SSL)
  • Encryption: SSL/TLS
  • Authentication: Basic (username/password)
  • Username: Full email address (******@domain.com)
  • Check "Require logon using Secure Password Authentication (SPA)" is unchecked

6. Check for Blocking Factors

• Verify the account isn't locked out in Active Directory
• Check if any security software is blocking POP3 traffic
• Review Exchange server logs for more detailed error information

7. Alternative Approach

If POP3 continues to fail, consider:

• Using IMAP instead (port 993 with SSL)
• Configuring MAPI/Outlook Anywhere (if Exchange allows it)

The "-ERR Server Unavailable. 21" typically indicates either a service not running or an authentication protocol mismatch. The most common fix is ensuring POP3 services may running and using Basic authentication with SSL on port 995.