Bitte prüfen, ob der POP-Proxy des Exchange läuft (Exchange Management Shell):

Get-ServerComponentstate -Identity Exchange-Server
 
Server                                  Component                               State
------                                  ---------                               -----
Exchange-Server.mydomain.local                  ServerWideOffline                       Active
Exchange-Server.mydomain.local                  HubTransport                            Active
Exchange-Server.mydomain.local                  FrontendTransport                       Active
Exchange-Server.mydomain.local                  Monitoring                              Active
Exchange-Server.mydomain.local                  RecoveryActionsEnabled                  Active
Exchange-Server.mydomain.local                  AutoDiscoverProxy                       Active
Exchange-Server.mydomain.local                  ActiveSyncProxy                         Active
Exchange-Server.mydomain.local                  EcpProxy                                Active
Exchange-Server.mydomain.local                  EwsProxy                                Active
Exchange-Server.mydomain.local                  ImapProxy                               Active
Exchange-Server.mydomain.local                  OabProxy                                Active
Exchange-Server.mydomain.local                  OwaProxy                                Active
Exchange-Server.mydomain.local                  PopProxy                                Inactive
Exchange-Server.mydomain.local                  PushNotificationsProxy                  Active
Exchange-Server.mydomain.local                  RpsProxy                                Active
Exchange-Server.mydomain.local                  RwsProxy                                Active
Exchange-Server.mydomain.local                  RpcProxy                                Active
Exchange-Server.mydomain.local                  UMCallRouter                            Active
Exchange-Server.mydomain.local                  XropProxy                               Active
Exchange-Server.mydomain.local                  HttpProxyAvailabilityGroup              Active
Exchange-Server.mydomain.local                  ForwardSyncDaemon                       Inactive
Exchange-Server.mydomain.local                  ProvisioningRps                         Inactive
Exchange-Server.mydomain.local                  MapiProxy                               Active
Exchange-Server.mydomain.local                  EdgeTransport                           Active
Exchange-Server.mydomain.local                  HighAvailability                        Active
Exchange-Server.mydomain.local                  SharedCache                             Active

Läuft der Proxy nicht, kann er mit Hilfe dieses Befehls wieder aktiviert werden:

Set-ServerComponentState -Identity Exchange-Server -Component PopProxy -Requester HealthAPI -State Active