Manual store / restore using Enterprise Vault (EV) Outlook Add-in fails with the error – “Enterprise Vault is currently unavailable. Try again later.”

Problem

Manual store / restore using EV Outlook Add-in fails with the error – “Enterprise Vault is currently unavailable. Try again later.”

Error Message

Manual store / restore using EV Outlook Add-in fails with the below pop-up window error:

Could not process the selected items.
Reason: Enterprise Vault is currently unavailable. Try again later.

EV Client trace shows the following:

24/04/2020 14:44:18.868[7460][H]: HTTP request error: 366 (503)
24/04/2020 14:44:18.868[7460][M]: HTTP request error. Enterprise Vault is currently unavailable. Try again later. 503

A Dtrace of w3wp from the EV Server handling the storage service for the corresponding user's mailbox archive will show the following:

(w3wp) <46256>               EV:M     CAutoAgentsOnline::RequestAction - Successfully Mapped A Task - VaultMachine [EUVLT01.EV.local]|TaskEntryID [13ECBDE352DC7BE4181B9ECDBF1DE751A1012000vault.EV.local.local]|Exchange [..EXCHSVRNOTREQD..]|Mailbox [/o=Veritas Lab/ou=US/cn=Recipients/cn=ABC]|FolderPath []
(w3wp) <46256>               EV:L     {VaultCreateInstanceRequest::CreateInstance} CLSID [{3342DB60-B74A-11D1-9E4B-0000F8789EA8} (EnterpriseVault.ExchangeArchivingAgentQueue.1)] Server Name [EUVLT01.EV.local.local] Used Server Name [EUVLT01.EV.local] Num of attempts [1] Total elapsed [1.267s] Result [Success  (0)]
(w3wp) <46256>               EV:L     {ClientAuthImpl::RegisterClientToken} Windows token [00000000], Flags [None (0x0)], AuthToken [FRMVLT01.EV.local sr676UL7FA*****]
(w3wp) <46256>               EV:L     CAuthHelper::Reset Cancel registration? True CancelId: 25828
(w3wp) <46256>               EV:H     {ClientAuthImpl::GetLocalAuthServer} (Exit) Status: [Exception]
(w3wp) <46256>               EV:L     {ClientAuthImpl::CancelClientIdentity} AuthToken [FRMVLT01.EV.local.local sr676UL7FA*****]. Token existed [True]
(w3wp) <46256>               EV:M     CAutoAgentsOnline::RequestAction - Com Result [0x80070721]

Cause

The behavior can be seen when EV Servers have been migrated to different hardware. The EV Server currently hosting the Archive Task for the corresponding mailbox and the EV Server handling the storage service for the mailbox archive resides on separate servers.

Solution

To get around this problem, some additional SPN's for Agentclientbroker and Storageonlineopns should be registered for all the EV servers.
 
Commands which can be used to register the SPN for the server are as follows and server names (Hostname, FQDN, EVServerAlias) should be replaced with the proper names for the environment:

setspn -a Agentclientbrokerserver/Hostname EVserviceaccount (Hostname of EV server)
setspn -a Agentclientbrokerserver/FQDN EVserviceaccount (FQDN of EV server)
setspn -a Agentclientbrokerserver/EVServerAlias EVserviceaccount (EVServerAlias.domain.com of EV server)

Example: setspn -a Agentclientbrokerserver/Hostname ev-exch

setspn -a Storageonlineopns/Hostname EVserviceaccount (Hostname of EV server)
setspn -a Storageonlineopns/ FQDN EVserviceaccount (FQDN of EV server)
setspn -a Storageonlineopns/ EVServerAlias EVserviceaccount (EVServerAlias.domain.com of EV server)

Example: setspn -a Storageonlineopns/Hostname ev-exch

Register the SPN's for all the other EV servers using the same command with relevant server name modifications as mentioned above.

To confirm the SPN's have been registered successfully, the below command format could be used to list them with the "accountname" parameter replaced by the target computer name, domain\name, or the user account:
setspn -L accountname

Example: setspn -L ev-exch