POP3 / IMAP4 not authenticating?

Hi All,

I've configured POP3 and IMAP4 on an Exchange server 2013 and it seems set to go but I just cannot authenticate with a valid UPN and valid password for the UPN.

Any Ideas what the heck I am missing???

+OK The Microsoft Exchange POP3 service is ready.
USER myname@mydomain.co.za
+OK
PASS MyPassword
-ERR Logon failure: unknown user name or bad password.

So I tried with 'USER mydomain\myname' and got same result. This occurs is both internally via TELNET on the exchange server IP and externally from a remote location over the mail record.

[PS] C:\Users\MyUsernameTest-PopConnectivity |fl

RunspaceId                      : f8b53262-35fb-421f-9a6e-9a96e1fc1e64
LocalSite                          : Default-First-Site-Name
SecureAccess                   : False
VirtualDirectoryName        :
Url                                   :
UrlType                            : Unknown
Port                                 : 995
ConnectionType                : Ssl
ClientAccessServerShortName : EX2013
LocalSiteShortName          : Default-First-Site-Name
ClientAccessServer          : EX2013.mydomain.co.za
Scenario                         : Test POP3 Connectivity
ScenarioDescription         : Connect to server using POP3 protocol, search for the test message, and delete it along
                                       with any messages that are older than 24 hours.
PerformanceCounterName      : POPConnectivity-Latency
Result                            :Failure
Error                              :POP Error: -ERR Logon failure: unknown user name or bad password.

UserName                    : extest_2a2410a5aa324
StartTime                   : 2/11/2016 10:07:35 AM
Latency                     : 00:00:02.1115573
EventType                   : Error
LatencyInMillisecondsString :
Identity                    :
IsValid                     : True
ObjectState                 : New