Enterprise Vault and Exchange Server: event 3305, archiving tasks, throttling, shortcuts

Enterprise Vault (EV) archives Exchange mailboxes by logging on to them as the Vault Service account, moving items into its own storage and leaving shortcuts behind. When a task won't start, stalls under load or leaves shortcuts users can't open, the cause is usually an Exchange-side prerequisite: the account's permissions, the EV system mailbox, the throttling policy or the client add-in. Here's how to check each on Exchange Server SE and Exchange 2019.

Symptoms#

The Exchange Mailbox Archiving task stops or won't start, and the Enterprise Vault event log shows Event ID 3305 (Enterprise Vault):

Event ID 3305 (Enterprise Vault)
The task Mailbox Archiving Task for EX01 failed to log on to Exchange server EX01 using mailbox EnterpriseVault-EX01. Please ensure that the server is running and that the Vault Service account has sufficient permissions on the server.

That wording comes from third-party event references rather than Arctera's documentation, so treat it as reported text: your task and mailbox names will differ, and it varies between EV versions (admins report a Journaling task variant that also asks you to check the mailbox hasn't been hidden). Other signs:

• New mailboxes are never enabled for archiving.
• Tasks start but fail or crawl when they process many mailboxes at once.
• Shortcuts open as plain messages, or the EV buttons are missing in Outlook or Outlook on the web.
• A manual mailbox synchronization never logs its "finished" event.

Why it happens#

EV's archiving tasks log on to Exchange mailboxes as the Vault Service account and rely on Outlook installed on the EV server. EV's guide lists the Exchange-side preparation, and each item maps to a failure when it's missing or later undone:

Throttling matters most: EV's guide says Exchange's default throttling policy restricts an account to 20 open connections, which would make the tasks that run under the Vault Service account fail.

How to fix it#

1. Check the account and the system mailbox#

$ev = "CONTOSO\svc-ev"
Get-Mailbox svc-ev | Format-List Name, Database, RecipientTypeDetails
Get-Mailbox "EnterpriseVault-EX01" | Format-List Name, Database, HiddenFromAddressListsEnabled
Get-ADPermission "EnterpriseVault-EX01" -User $ev | Where-Object { $_.ExtendedRights -like "*Send*" }

Use the system mailbox named in the task's properties. Both mailboxes must exist on mounted databases, and the last command must return a Send As entry. Admins also report event 3305 after the system or journal mailbox was hidden from address lists, so note HiddenFromAddressListsEnabled too. If Send As is missing:

Add-ADPermission -Identity "EnterpriseVault-EX01" -User $ev -ExtendedRights "Send As"

2. Check the Exchange permissions#

Get-MailboxDatabase | Get-ADPermission -User $ev | Format-Table Identity, Deny, AccessRights, ExtendedRights -AutoSize

Compare the output with the "Microsoft Exchange permissions assigned to the Vault Service account" topic for your EV version, and re-run EV's permission procedure for any server or database added since EV was installed. Check the Deny column too: a deny reaching the account directly or through a group can block mailbox access — one more reason to keep the Vault Service account out of admin groups (see Exchange Server RBAC).

3. Apply EV's throttling policy#

Get-ThrottlingPolicyAssociation svc-ev | Format-List Name, ThrottlingPolicyId

An empty ThrottlingPolicyId means the default policy applies. Copy SetEVThrottlingPolicy.ps1 from the PowerShell Scripts folder on the EV media to an Exchange server and run it in the Exchange Management Shell; it creates a policy and assigns it to the Vault Service account (-server names a mailbox server when run remotely). Use an account with the Mail Recipients and Recipient Policies roles, which Organization Management has. If tasks run under another service account, target that account; cross-forest, specify the resource domain so the linked mailbox is updated.

The change can take up to two hours. To apply it now, restart the Microsoft Exchange RPC Client Access service on each Exchange server, then confirm:

Restart-Service MSExchangeRPC
Get-ThrottlingPolicyAssociation svc-ev | Format-List Name, ThrottlingPolicyId

4. Check the EV server and domain controllers#

• Keep Outlook on the EV server at a version your EV release supports (EV's compatibility charts list them), and make sure the Vault Service account can still log on there with its user profile intact.
• Apply EV's step "Removing the restriction on NSPI connections to a Windows Server domain controller" on the domain controllers EV uses. It's a change on the DCs themselves, so follow the guide exactly and plan it with your AD team.
• Check the Exchange Provisioning task: new mailboxes must be processed by it before they can be enabled, so confirm a provisioning task covers their domain and provisioning group and completes without errors. If it runs under an account other than the Vault Service account, check that account's EV role and permissions against the guide.

5. Fix shortcuts that don't open#

• In Outlook, shortcut handling and the EV buttons come from the EV Outlook add-in. Check File › Options › Add-ins (the COM Add-ins and Disabled Items lists); if Outlook keeps disabling it, update the EV client to a build supported with that Outlook version.
• Opening an archived item retrieves it from the EV server, so test from the user's device that the EV server's web address loads without certificate or proxy errors.
• Works in Outlook but not Outlook on the web? Compare your EV version's documented Outlook on the web support with your Exchange build — that's EV client-access configuration, not a mailbox fault.

Verify the fix#

• Start the task: no new event 3305 appears.
• In the Vault Administration Console, open the Mailbox Archiving Task's properties and run a synchronization of all mailboxes from the Synchronization tab. The Enterprise Vault event log should record the run starting and finishing for the Exchange server, with no logon errors in between.
• A Report Mode run shows what the task would archive; then let a scheduled run archive a test mailbox.
• Get-ThrottlingPolicyAssociation shows the EV policy for the Vault Service account.
• A new shortcut opens in Outlook and, where supported, in Outlook on the web.

Key takeaways#

• Event 3305 means the task couldn't log on: check the system mailbox, Send As and permissions first.
• Give the account EV's own throttling policy and restart RPC Client Access to apply it.
• Re-run EV's Exchange permission steps whenever you add servers or databases, including during a move to Exchange Server SE.
• Shortcut problems are usually the add-in or reachability of the EV server, not Exchange. If EV also archives a journal mailbox, see journaling to a third-party archive for the Exchange side of journaling.

References#

• Preinstallation tasks for Exchange server archiving (Enterprise Vault 15.2 Installing and Configuring)
• Configuring the Exchange throttling policy on the Vault Service account (Enterprise Vault Installing and Configuring)
• EWS throttling in Exchange: how throttling policies apply (Microsoft Learn)