Manage mailbox auditing

Mailbox audit logging is turned on by default in all organizations. This setting automatically logs certain actions that mailbox owners, delegates, and admins perform. Admins can search the mailbox audit log for the corresponding mailbox audit records.

Some benefits of mailbox auditing on by default include:

• Auditing is automatically turned on when you create a new mailbox. You don't need to manually enable mailbox auditing for new users.
• You don't need to manage the mailbox actions that are audited. A predefined set of mailbox actions are audited by default for each sign-in type (Admin, Delegate, and Owner).
• When Microsoft releases a new mailbox action, the action might be added automatically to the list of mailbox actions that are audited by default (subject to the user having the appropriate license). This result means you don't need to add new actions on mailboxes as they're released.
• You have a consistent mailbox auditing policy across your organization because you're auditing the same actions for all mailboxes.

Verify mailbox auditing on by default is turned on

To verify that mailbox auditing on by default is turned on for your organization, run the following command in Exchange Online PowerShell:

Get-OrganizationConfig | Format-List AuditDisabled

The value False indicates that mailbox auditing on by default is turned on for the organization. Mailbox auditing on by default in the organization overrides the mailbox auditing settings on individual mailboxes. For example, if mailbox auditing is turned off for a mailbox (the AuditEnabled property on the mailbox is False), the default mailbox actions are still audited for the mailbox because mailbox auditing on by default is turned on for the organization.

To keep mailbox auditing disabled for specific mailboxes, configure mailbox auditing bypass for the mailbox owner and other users with delegated access to the mailbox. For more information, see the Bypass mailbox audit logging section later in this article.

Supported mailbox types

The following table describes mailbox types that mailbox auditing supports by default:

Sign-in types and mailbox actions

Sign-in types classify who's responsible for the audited actions on the mailbox. The following list describes the sign-in types that mailbox audit logging uses:

• Owner: The mailbox owner (the account associated with the mailbox).
• Delegate:
  • A user assigned the SendAs, SendOnBehalf, or FullAccess permission to another mailbox.
  • An admin assigned the FullAccess permission to a user's mailbox.
• Admin:
  • The mailbox is searched with one of the following Microsoft eDiscovery tools:
    • eDiscovery in the Microsoft Purview portal.
    • In-Place eDiscovery in Exchange Online.
  • The mailbox is accessed by using the Microsoft Exchange Server MAPI Editor.
  • The mailbox is accessed by an account impersonating another user. This access happens when the ApplicationImpersonation role is assigned to an account, such as an application, which is now actively accessing the data. For more information, see Configure impersonation.

Mailbox actions for user mailboxes and shared mailboxes

The following table describes the mailbox actions that are available in mailbox audit logging for user mailboxes and shared mailboxes.

• A check mark (✔) indicates the mailbox action can be logged for the sign-in type (not all actions are available for all sign-in types).
• An asterisk ( ^* ) after the check mark indicates the mailbox action is logged by default for the sign-in type.
• Remember, an admin with Full Access permission to a mailbox is considered a delegate.

Mailbox actions for Microsoft 365 Group mailboxes

When you turn on mailbox auditing, Microsoft 365 Group mailboxes start logging mailbox audit data. However, you can't customize the logged data or add or remove mailbox actions for any sign-in type.

The following table describes the mailbox actions that Microsoft 365 Group mailboxes log by default for each sign-in type.

Remember, an admin with Full Access permission to a Microsoft 365 Group mailbox is considered a delegate.

Verify that default mailbox actions are being logged for each sign-in type

When mailbox auditing is enabled by default, the system adds a DefaultAuditSet property to all mailboxes. This property's value shows whether the default mailbox actions (managed by Microsoft) are audited on the mailbox.

To see the value for user mailboxes or shared mailboxes, replace <MailboxIdentity> with the name, alias, email address, or user principal name (username) of the mailbox and run the following command in Exchange Online PowerShell:

Get-Mailbox -Identity <MailboxIdentity> | Format-List DefaultAuditSet

To see the value for Microsoft 365 group mailboxes, replace <MailboxIdentity> with the name, alias, or email address of the shared mailbox and run the following command in Exchange Online PowerShell:

Get-Mailbox -Identity <MailboxIdentity> -GroupMailbox | Format-List DefaultAuditSet

The value Admin, Delegate, Owner means:

• The default mailbox actions for all three sign-in types are audited. This value is the only value you see on Microsoft 365 Group mailboxes.
• An admin didn't change the audited mailbox actions for any sign-in type on a user mailbox or a shared mailbox.

If an admin changes the mailbox actions that are audited for a sign-in type (by using the AuditAdmin, AuditDelegate, or AuditOwner parameters on the Set-Mailbox cmdlet), the property value is different.

For example, the value Owner for the DefaultAuditSet property on a user mailbox or shared mailbox means:

• The default mailbox actions for the mailbox owner are audited.
• The audited mailbox actions for the Delegate and Admin sign-in types are changed from the default actions.

A blank value for the DefaultAuditSet property means the mailbox actions for all three sign-in types are changed on the user mailbox or a shared mailbox.

For more information, see the Change or restore mailbox actions logged by default section in this article.

Display the mailbox actions that are being logged on mailboxes

To see the mailbox actions that are currently being logged on user mailboxes or shared mailboxes, replace <MailboxIdentity> with the name, alias, email address, or user principal name (username) of the mailbox, and run one or more of the following commands in Exchange Online PowerShell.

Owner actions

Get-Mailbox -Identity <MailboxIdentity> | Select-Object -ExpandProperty AuditOwner

Delegate actions

Get-Mailbox -Identity <MailboxIdentity> | Select-Object -ExpandProperty AuditDelegate

Admin actions

Get-Mailbox -Identity <MailboxIdentity> | Select-Object -ExpandProperty AuditAdmin

Change or restore mailbox actions logged by default

As previously explained, one of the key benefits of having mailbox auditing on by default is that you don't need to manage the mailbox actions that are audited. Microsoft manages the actions for you, and automatically adds new mailbox actions to be audited by default as they're released.

However, your organization might be required to audit a different set of mailbox actions for user mailboxes and shared mailboxes. The procedures in this section show you how to change the mailbox actions that are audited for each sign-in type, and how to revert back to the Microsoft-managed default actions.

Change the mailbox actions to audit

Use the AuditAdmin, AuditDelegate, or AuditOwner parameters on the Set-Mailbox cmdlet to change the mailbox actions that Microsoft audits for user mailboxes and shared mailboxes. You can't customize audited actions for Microsoft 365 group mailboxes.

Use two different methods to specify the mailbox actions:

• Replace (overwrite) the existing mailbox actions by using this syntax: action1,action2,...actionN.
• Add or remove mailbox actions without affecting other existing values by using this syntax: @{Add="action1","action2",..."actionN"} or @{Remove="action1","action2",..."actionN"}.

The following example changes the admin mailbox actions for the mailbox named "Gabriela Laureano" by overwriting the default actions with SoftDelete and HardDelete.

Set-Mailbox -Identity "Gabriela Laureano" -AuditAdmin HardDelete,SoftDelete

The following example adds the MailboxLogin owner action to the mailbox laura@contoso.onmicrosoft.com.

Set-Mailbox -Identity laura@contoso.onmicrosoft.com -AuditOwner @{Add="MailboxLogin"}

The following example removes the MoveToDeletedItems delegate action for the Team Discussion mailbox.

Set-Mailbox -Identity "Team Discussion" -AuditDelegate @{Remove="MoveToDeletedItems"}

Regardless of the method you use, customizing the audited mailbox actions on user mailboxes or shared mailboxes has the following results:

• Microsoft no longer manages the audited mailbox actions for the sign-in type that you customized.
• The sign-in type that you customized no longer appears in the DefaultAuditSet property value for the mailbox as previously described.

Restore the default mailbox actions

If you customized the mailbox actions that are audited on a user mailbox or a shared mailbox, you can restore the default mailbox actions for one or all sign-in types by using this syntax:

Set-Mailbox -Identity <MailboxIdentity> -DefaultAuditSet <Admin | Delegate | Owner>

You can specify multiple DefaultAuditSet values separated by commas.

This example restores the default audited mailbox actions for all sign-in types on the mailbox mark@contoso.onmicrosoft.com.

Set-Mailbox -Identity mark@contoso.onmicrosoft.com -DefaultAuditSet Admin,Delegate,Owner

This example restores the default audited mailbox actions for the Admin sign-in type on the mailbox chris@contoso.onmicrosoft.com, but keeps the customized audited mailbox actions for the Delegate and Owner sign-in types.

Set-Mailbox -Identity chris@contoso.onmicrosoft.com -DefaultAuditSet Admin

Restoring the default audited mailbox actions for a sign-in type results in the following outcomes:

• The current list of mailbox actions is replaced with the default mailbox actions for the sign-in type.
• Any new mailbox actions that Microsoft releases are automatically added to the list of audited actions for the sign-in type.
• The DefaultAuditSet property value for the mailbox is updated to include the restored sign-in type.

Turn off mailbox auditing on by default for your organization

To turn off mailbox auditing on by default for your entire organization, run the following command in Exchange Online PowerShell:

Set-OrganizationConfig -AuditDisabled $true

When you turn off mailbox auditing on by default, you make the following changes:

• Mailbox auditing is turned off for your organization.
• From the time you turn off mailbox auditing on by default, no mailbox actions are audited, even if mailbox auditing is enabled on a mailbox (the AuditEnabled property on the mailbox is True).
• Mailbox auditing isn't turned on for new mailboxes and setting the AuditEnabled property on a new or existing mailbox to True is ignored.
• Any mailbox audit bypass association settings (configured by using the Set-MailboxAuditBypassAssociation cmdlet) are ignored.
• Existing mailbox audit records are retained until the audit log age limit for the record expires.

Turn on mailbox auditing on by default

To turn mailbox auditing back on for your organization, run the following command in Exchange Online PowerShell:

Set-OrganizationConfig -AuditDisabled $false

Bypass mailbox audit logging

Currently, you can't disable mailbox auditing for specific mailboxes when mailbox auditing on by default is turned on in your organization. For example, the system ignores setting the AuditEnabled mailbox property to False.

However, you can use the Set-MailboxAuditBypassAssociation cmdlet in Exchange Online PowerShell to prevent all mailbox actions by the specified users from being logged, regardless of where the actions occur. For example:

• Mailbox owner actions that the bypassed users perform aren't logged.
• Delegate actions that the bypassed users perform on other users' mailboxes (including shared mailboxes) aren't logged.
• Admin actions that the bypassed users perform aren't logged.

To bypass mailbox audit logging for a specific user, replace <MailboxIdentity> with the name, email address, alias, or user principal name (username) of the user and run the following command:

Set-MailboxAuditBypassAssociation -Identity <MailboxIdentity> -AuditByPassEnabled $true

To verify that auditing is bypassed for the specified user, run the following command:

Get-MailboxAuditBypassAssociation -Identity <MailboxIdentity> | Format-List AuditByPassEnabled

The value True indicates that mailbox audit logging is bypassed for the user.

More information

• By default, mailbox audit log records are retained for 90 days before they're deleted. You can change the age limit for audit log records by using the AuditLogAgeLimit parameter on the Set-Mailbox cmdlet in Exchange Online PowerShell. However, increasing this value doesn't enable you to search for events that are older than 90 days in the audit log.

• If you change the AuditLogAgeLimit property for a mailbox before turning on mailbox auditing by default for the organization, the mailbox's existing audit log age limit remains unchanged. In other words, mailbox auditing by default doesn't affect the current age limit for mailbox audit records.

• To change the AuditLogAgeLimit value on a Microsoft 365 Group mailbox, include the -GroupMailbox switch in the Set-Mailbox command.

• Mailbox audit log records are stored in a subfolder (named Audits) in the Recoverable Items folder in each user's mailbox. Keep the following things in mind about mailbox audit records and the Recoverable Items folder:

  • Mailbox audit records count against the storage quota of the Recoverable Items folder, which is 30 GB by default (the warning quota is 20 GB). The storage quota automatically increases to 100 GB (with a 90-GB warning quota) when:

    • You place a hold on a mailbox.
    • You assign the mailbox to a retention policy in the Microsoft Purview portal.

  • Mailbox audit records also count against the folder limit for the Recoverable Items folder. A maximum of 3 million items (audit records) can be stored in the Audits subfolder.

    Note

    It's unlikely that mailbox auditing by default impacts the storage quota or the folder limit for the Recoverable Items folder.

    • You can run the following command in Exchange Online PowerShell to display the size and number of items in the Audits subfolder in the Recoverable Items folder:

      Get-MailboxFolderStatistics -Identity <MailboxIdentity> -FolderScope RecoverableItems | Where-Object {$_.Name -eq 'Audits'} | Format-List FolderPath,FolderSize,ItemsInFolder
      

    • You can't directly access an audit log record in the Recoverable Items folder. Instead, use the Search-UnifiedAuditLog cmdlet or search the audit log to find and view mailbox audit records.

• If you place a mailbox on hold or assign it to a retention policy, audit log records are still retained for the duration defined by the mailbox's AuditLogAgeLimit property (90 days by default). To retain audit log records longer for mailboxes on hold, increase the mailbox's AuditLogAgeLimit value.

• In a multi-geo environment, cross-geo mailbox auditing isn't supported. For example, if you assign a user permissions to access a shared mailbox in a different geo ___location, mailbox actions that the user performs aren't logged in the mailbox audit log of the shared mailbox. Exchange admin audit events are available for all locations via Microsoft Purview and the Search-UnifiedAuditLog cmdlet.