Exchange Error: The handshake failed due to an unexpected packet format


A customer reported inoperative IMAP functionality for some user mailboxes. I checked all CAS servers and discovered the following issue with one of them:

[PS] C:\>Test-ImapConnectivity -ClientAccessServer ServerEx10a|fl

RunspaceId                  : ad18027f-3e0f-44c2-a192-ff24b54e0680
LocalSite                   : Contoso-office
SecureAccess                : False
VirtualDirectoryName        :
Url                         :
UrlType                     : Unknown
Port                        : 993
ConnectionType              : Ssl
ClientAccessServerShortName : ServerEx10a
LocalSiteShortName          : Contoso-office
ClientAccessServer          : ServerEx10a.contoso.net
Scenario                    : Test IMAP4 Connectivity
ScenarioDescription         : Connect to server using IMAP4 protocol, search for the test message, and delete it along
                              with any messages that are older than 24 hours.
PerformanceCounterName      : ImapConnectivity-Latency
Result                      : Failure
Error                       : Microsoft.Exchange.Monitoring.ProtocolException: Authentication failed. The connection is
                               being closed.
                              The handshake failed due to an unexpected packet format.Server response while making conn
                              ection:[]. ---> System.IO.IOException: The handshake failed due to an unexpected packet f
                              ormat.
UserName                    : extest_f865f9d53e494
StartTime                   : 2/13/2014 9:11:03 AM
Latency                     : 00:00:00.0144858
EventType                   : Error
LatencyInMillisecondsString :
Identity                    :
IsValid                     : True

Error “Microsoft.Exchange.Monitoring.ProtocolException: Authentication failed. The connection is being closed. The handshake failed due to an unexpected packet format. Server response while making connection:[]. —> System.IO.IOException: The handshake failed due to an unexpected packet format.” was due to the missing intermediate certification authority (CA) certificate. I unified the cert (export/import) among CAS servers to get it fixed.

4- 3- 2014 21-07-41Exchange 2010 – Understanding POP3 and IMAP4

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