MailItemsAccessed Throttling [Nobelium]

id: 67c763f7-c4fd-4b0f-9d4b-19246d1ec6d7
name: MailItemsAccessed Throttling [Nobelium]
description: |
  The MailItemsAccessed action is part of the new Advanced Audit functionality of Microsoft Defender XDR. It's part of Exchange mailbox auditing and is enabled by default for users that have an Office 365 or Microsoft 365 E5 license, or for organizations with a Microsoft 365 E5 Compliance add-on subscription.
  If more than 1,000 MailItemsAccessed audit records are generated in less than 24 hours, Exchange Online will stop generating auditing records for MailItemsAccessed activity. When a mailbox is throttled, MailItemsAccessed activity will not be logged for 24 hours after the mailbox was throttled. If this occurs, there's a potential that mailbox could have been compromised during this period. The recording of MailItemsAccessed activity will be resumed following a 24-hour period.
  The query is looking for MailItemsAccessed Throttling events where the operation is done by a ClientApplication.
  See The MailItemsAccessed mailbox auditing action.
  Reference - https://docs.microsoft.com/microsoft-365/compliance/mailitemsaccessed-forensics-investigations?view=o365-worldwide#the-mailitemsaccessed-mailbox-auditing-action
requiredDataConnectors:
- connectorId: MicrosoftThreatProtection
  dataTypes:
  - CloudAppEvents
tactics:
- Exfiltration
tags:
- Nobelium
query: |
  let starttime = 1d;
  CloudAppEvents
  | where Timestamp between (startofday(ago(starttime))..now())
  | where ActionType == "MailItemsAccessed"
  | extend isThrottled=RawEventData['OperationProperties'][1]
  | where isnotempty(RawEventData['ClientAppId'] ) and isThrottled has "True" and RawEventData['AppId'] has "00000003-0000-0000-c000-000000000000"//GrapAPI Id
  | project Timestamp, RawEventData['OrganizationId'],AccountObjectId,UserAgent