Users cannot connect to POP3 or IMAP4

Original KB number:   3025138

Symptom 1

Users who have a mailbox on Exchange Server 2016 or Exchange Server 2013 may find that their connections to POP3 or IMAP4 stop working. Additionally, they may receive the following error message:

Microsoft.Exchange.Monitoring.ProtocolException: Authentication failed.
The connection is being closed. Unable to read data from the transport connection: An
existing connection was forcibly closed by the remote host.Server response while making
connection:[]. ---> System.IO.IOException: Unable to read data from the transport
connection: An existing connection was forcibly closed by the remote host. --->
System.Net.Sockets.SocketException: An existing connection was forcibly closed by the
remote hostThe related service are started, no error/warning events in system or
application log.

Symptom 2

Users can telnet to a POP3 or IMAP port by using the server FQDN. However, they don't see the banner. Instead, they see only a blank screen.

Cause

This issue occurs because the PopProxy and ImapProxy components are in inactive state.

You can use the Get-ServerComponentState <ServerName> command to check on the status of components.

Resolution

To resolve this issue, make the PopProxy and ImapProxy components active. To do this, follow these steps:

1. Use the following command to determine which requester made PopProxy inactive:

   Get-ServerComponentState -Identity <ServerName> -Component PopProxy).LocalStates

   In the following example, HealthAPI is displayed as the requester that changed the state of PopProxy to Inactive.

   

2. Use the following command to make PopProxy active:

   Set-ServerComponentState -Identity <ServerName> -component PopProxy -state Active -requester HealthAPI

   For example: