The following is provided from Microsoft Security and Compliance blogs at TechCommunity:

After listening to customer feedback and suggestions, Exchange Online is making some key changes to the mailbox auditing feature for Office 365 commercial users.

1. Mailbox audits will be stored for all user mailboxes within the commercial service by default.
2. The default audit configuration will change and include more audit events.

 

Why is this change happening?

These enhancements and modifications are a part of Microsoft’s commitments to improve the security tooling available to our customers and to ensure that our customers have access to critical audit data to investigate security incidents in their environment when required.

 

Enabling mailbox auditing by default addresses a specific pain-point with mailbox audit administration today, as Exchange administrators must configure the AuditEnabled setting on each mailbox to be audited after it is provisioned.  In support of Microsoft’s commitment to providing our customers with an easy-to-use set of security features, Customers will no longer be required to configure mailbox auditing on a per-mailbox basis, and instead will be able rely on a tenant-wide configuration to enable or disable mailbox audit event collection.  Mailbox events will be stored on the all user mailboxes automatically without required action.

 

In addition, we plan to expand the default set of audit actions to include more of the currently available Owner and Delegate events. If your mailbox configurations rely on the default settings for AuditOwner, AuditDelegate and AuditAdmin actions, your mailboxes will begin to audit according to the updated defaults. If your Exchange administrator has in the past configured mailboxes with a different set of distinct events, those mailboxes will still follow the configuration that was elected and will not be overridden.   We are frequently adding to the available mailbox audit actions, and as we continue to add audit capabilities, these audit actions will be added to the default as well. A recent example was the introduction of the audit action for the creation of new Inbox Rules and Calendar delegation settings. We believe that auditing these actions can help our customers trace activity on the mailboxes within their service to a more complete degree. 

 

When will this happen, and what do I need to do?

Over the next several months, we will enable the default-auditing configuration on all tenants with a steady ramp-up with all commercial customers to be covered by the end of the calendar year.  At that time, there is nothing you need to do for the service to begin storing your user’s audit events. And if you have already enabled mailbox auditing in Exchange on your user’s mailboxes and are doing so for all new mailboxes – great! Mailboxes that are configured to audit today will continue to do so.

 

If the Exchange mailbox audit feature is new to you, please take some time to familiarize yourself with the options for mailbox auditing and learn how to leverage these events for your security investigation scenarios. Mailboxes generating audit records can be found in the Security & Compliance Center’s Audit Log interface, or in the mailbox audit log through the Search-MailboxAuditLog cmdlet. Additionally, explore the options available to you for audit actions including the newly-available ones. If you do not intend on relying on the default configuration, consider adding the new audit actions to your configured set.

 

How can I opt-out of default mailbox auditing?

As we begin rolling out the default-on configuration to tenants worldwide, a tenant administrator has the capability to pre-emptively override and disable all mailbox audits within their tenancy with the Set-OrganizationConfig cmdlet. You may choose to proactively prevent your tenancy’s mailboxes from being audited as part of this feature introduction with this setting. If the tenant-wide AuditDisabled setting is true, all settings for mailbox audit will be overridden to ignore audits. We don’t recommend you use this – but is available should your business require it.

 

What actions are recordable with Mailbox Auditing?

Mailbox auditing for Owner actions includes high-value scenarios to investigating a business email compromise, such as:

• MailboxLogin events – these events are recorded with client access to user mailboxes including protocol access with POP and IMAP
• Mail actions to Create, Update (edit) a message in any folder, delete actions to include moving a message to the Deleted Items folder or permanently removing messages, and the Copy or Move of a message.  
• Actions commonly used in attack scenarios: creation of a mailbox’s Inbox Rule, adding Delegates, or delegating Calendar access to another user.

These Owner events will be added to the service’s default mailbox configuration for auditing. Additional events auditable for the mailbox’s Delegation capabilities include further valuable scenarios that will also be added as default:

• Mails sent on behalf of an individual, in addition to the SendAs action that is currently default
• A Delegate’s action to delete messages in a user’s mailbox or move them around folders.

 

How do I….?

Make Modifications to the Audit Actions

If you choose not to rely on the default settings for audit actions, you may add or drop actions from your configuration with the Set-Mailbox cmdlet for individual mailboxes. Once you elect a set of audit events this way, your mailboxes will no longer automatically follow the default service configuration and will need to be updated via PowerShell when Exchange releases new auditable actions.

 

Disable Mailbox Auditing for All Mailboxes

When your organization begins auditing all mailboxes by default, you may disable all mailbox auditing with this command:

Set-OrganizationConfig -AuditDisabled $true

To re-enable all mailbox audits, run:

Set-OrganizationConfig -AuditDisabled $false

 

In the default setting, the -AuditDisabled value will be False.

 

Disable Mailbox Auditing on Some Mailboxes

When your tenancy begins auditing all mailboxes by default, the per-mailbox AuditEnabled setting will be overridden. However, you may still choose to disable audits for a subset of your users if there is a business need. You can elect this option by configuring audit bypass associations on the identities you intend to ignore with the Set-MailboxAuditBypassAssociation cmdlet.

 

Find more information:

• Search the audit log through the Security & Compliance center: https://support.office.com/en-us/article/Search-the-audit-log-in-the-Office-365-Security-Compliance-Center-0d4d0f35-390b-4518-800e-0c7ec95e946c
• About mailbox auditing: https://support.office.com/en-us/article/enable-mailbox-auditing-in-office-365-aaca8987-5b62-458b-9882-c28476a66918
• Set-OrganizationConfig commandlet: https://docs.microsoft.com/en-us/powershell/module/exchange/organization/set-organizationconfig?view=exchange-ps
• Set-MailboxAuditBypassAssociation commandlet: https://docs.microsoft.com/en-us/powershell/module/exchange/policy-and-compliance-audit/set-mailboxauditbypassassociation?view=exchange-ps
• Search-MailboxAuditLog commandlet: https://docs.microsoft.com/en-us/powershell/module/exchange/policy-and-compliance-audit/search-mailboxauditlog?view=exchange-ps
• Use the Office365 Management Activity API: https://msdn.microsoft.com/en-us/office-365/office-365-management-activity-api-reference

 

The above was provided from Microsoft Security and Compliance blogs at TechCommunity