Message policy and compliance

Archiving Exchange Online-based mailboxes

Exchange Online mailboxes reside in the cloud, and archiving them requires unique hosting environments. In some cases, Exchange Online can also be used to archive on-premises mailboxes in the cloud. The options for archiving with Exchange Online are described in this section.

Exchange Online provides built-in archiving capabilities for cloud-based mailboxes, including an In-Place Archive that gives users a convenient place to store older email messages. An In-Place Archive is a special type of mailbox that appears alongside a user's primary mailbox folders in Outlook and Outlook on the web. Users can access and search the archive in the same way they access and search their primary mailboxes. Available functionality depends on the client in use:

  • Outlook 2016, Outlook 2013, Outlook 2010, and Outlook on the web Users have access to the full features of the archive, as well as related compliance features like control over retention and archive policies.

  • Outlook 2007 Users have basic support for the In-Place Archive, but not all archiving and compliance features are available. For example, users cannot apply retention or archive policies to mailbox items and must rely on administrator-provisioned policies instead.

Administrators use the Exchange admin center or remote Windows PowerShell to enable the personal archive feature for specific users.

For more information, see:

Archive sizes

Only one user's messaging data can be stored in each personal archive. The allocation of storage depends on the subscription plan. For more information about archive mailbox sizes, see the "Mailbox storage limits" section in Exchange Online limits.


  • Using journaling, transport rules, or auto-forwarding rules to copy messages to an Exchange Online mailbox for the purposes of archiving is not permitted. Microsoft reserves the right to deny additional archive storage in instances where a mailbox archive is not being used in a personal scenario or in other cases of inappropriate use.
  • In-Place Archive has specific licensing requirements for Outlook users. Outlook 2007 users must have the Office 2007 Cumulative Update for February 2011 to access the personal archive.
  • Exchange Online does not support the New-MailboxImportRequest Windows PowerShell cmdlet of Exchange Server 2010 Service Pack 1 or later for administrator-driven import of .pst files into a personal archive. If a user has both the primary mailbox and the archive in Exchange Online, an administrator can use PST Capture, a free tool, to import .pst file data to the user's primary mailbox or archive.

Cloud-based archiving of on-premises mailboxes

Using Exchange Online for cloud-based archiving of on-premises Exchange Server 2010 or later mailboxes is possible with Microsoft Exchange Online Archiving, a hosted archiving solution from Microsoft. This requires that the on-premises organization be in Hybrid mode or be set up for Exchange Online Archiving.


Users with an on-premises mailbox on an Exchange 2010 Mailbox server who have a Managed Folder policy applied cannot have an on-premises or cloud-based In-Place Archive enabled.

Retention tags and retention policies

Exchange Online offers retention policies to help organizations reduce the liabilities associated with email and other communications. With these policies, administrators can apply retention settings to specific folders in users' inboxes. Administrators can also give users a menu of retention policies and let them apply the policies to specific items, conversations, or folders using Outlook 2010 or later or Outlook on the web.

In Exchange Online, administrators manage retention policies by using the Exchange admin center (EAC) or remote Windows PowerShell.

Exchange Online offers two types of policies: archive policies and delete policies. Both types can be combined on the same item or folder. For example, a user can tag an email message to be automatically moved to the In-Place Archive in a specified number of days and deleted after another span of days.

With Outlook 2010 or later and Outlook on the web, users can apply retention policies to folders, conversations, or individual messages. They can also view the applied retention policies and expected deletion dates on messages. Users of other email clients can only have email messages deleted or archived based on server-side retention policies set by the administrator.

The retention policy capabilities offered in Exchange Online are the same as those offered in Exchange Server 2010 Service Pack 2 RU4. Administrators can use remote Windows PowerShell to migrate retention policies from on-premises Exchange Server 2010 or later environments to Exchange Online.


Managed Folders, an older approach to messaging records management that was introduced in Exchange Server 2007, are not available in Exchange Online.

For more information, see Retention Tags and Retention Policies.

Encryption of data at rest

Encryption of customer data at rest is provided by multiple service-side technologies, including BitLocker, DKM, Azure Storage Service Encryption, and service encryption in Exchange Online, Skype for Business, OneDrive for Business, and SharePoint Online. Office 365 Service Encryption include an option to use customer-managed encryption keys that are stored in Azure Key Vault. This customer-managed key option, called Customer Key, is available for Exchange Online, SharePoint Online, and OneDrive for Business.


Microsoft servers use BitLocker to encrypt the disk drives containing customer data at rest at the volume-level. BitLocker encryption is a data protection feature that is built into Windows. BitLocker is one of the technologies used to safeguard against threats in case there are lapses in other processes or controls (e.g., access control or recycling of hardware) that could lead to someone gaining physical access to disks containing customer data. In this case, BitLocker eliminates the potential for data theft or exposure because of lost, stolen, or inappropriately decommissioned computers and disks.

Distributed Key Manager

In addition to BitLocker, we use a technology called Distributed Key Manager (DKM). DKM is a client-side functionality that uses a set of secret keys to encrypt and decrypt information. Only members of a specific security group in Active Directory Domain Services can access those keys to decrypt the data that is encrypted by DKM. In Exchange Online, only certain service accounts under which the Exchange processes run are part of that security group. As part of standard operating procedure in the datacenter, no human is given credentials that are part of this security group and therefore no human has access to the keys that can decrypt these secrets.

Customer Key

With Customer Key, you control your organization's encryption keys and then configure them to encrypt your data at rest in Microsoft's datacenters. Data at rest includes data from Exchange Online and Skype for Business that is stored in mailboxes and files that are stored in SharePoint Online and OneDrive for Business. For more information, see Controlling your data in using Customer Key and Service Encryption with Customer Key FAQ.

Office 365 Message Encryption

Office 365 Message Encryption allows email users to send encrypted email messages to anyone. We announced new capabilities in Office Message Encryption that leverage the protection features in Azure Information Encryption. These new capabilities provided enhanced end user experiences that make it easier to share and collaborate on protected messages with anyone inside or outside the organization. The new Office Message Encryption capabilities have some setup requirements. See Set up new Office 365 Message Encryption capabilities built on top of Azure Information Protection. Customers on legacy Office 365 Message Encryption do not get the new capabilities without following the set up guidance provided above. Please read the FAQ for more details on what's included in the new vs. legacy Office 365 Message Encryption capabilities.

Office 365 Advanced Message Encryption provides additional protection by allowing message expiration and revocation. You can also create multiple templates for encrypted emails originating from your organization. Advanced Message Encryption is included in Microsoft 365 E5, Office 365 E5, Microsoft 365 E5 (Nonprofit Staff Pricing), Office 365 Enterprise E5 (Nonprofit Staff Pricing), or Office 365 Education A5. If your organization has a subscription that does not include Office 365 Advanced Message Encryption, you can purchase Microsoft 365 E5 Compliance or the Office 365 Advanced Compliance SKU as an add-on.

Secure/Multipurpose Internet Mail Extensions (S/MIME)

S/MIME allows you to help protect sensitive information by sending signed and encrypted email within your organization. Administrators can use remote Windows PowerShell to set up S/MIME after establishing and issuing PKI certificates to users. These certificates must be synchronized from an on-premises Active Directory Certificate Service.

S/MIME is supported on Microsoft Edge and Internet Explorer 11. Currently, S/MIME is unsupported on Firefox, Opera, and Chrome. For more information, see S/MIME for Message Signing and Encryption.

In-Place Hold and Litigation Hold

When a reasonable expectation of litigation exists, organizations are required to preserve electronically stored information (ESI), including email that's relevant to the case. This expectation can occur before the specifics of the case are known, and preservation is often broad. Organizations may preserve all email related to a specific topic, or all email for certain individuals.

In Exchange Online, you can use In-Place Hold or Litigation Hold to accomplish the following goals:

  • Enable users to be placed on hold and preserve mailbox items immutably

  • Preserve mailbox items deleted by users or automatic deletion processes such as MRM

  • Protect mailbox items from tampering, changes by a user, or automatic processes by saving a copy of the original item

  • Preserve items indefinitely or for a specific duration

  • Keep holds transparent from the user by not having to suspend MRM

  • Use In-Place eDiscovery to search mailbox items, including items placed on hold

Additionally, you can use In-Place Hold to:

  • Search and hold items matching specified criteria

  • Place a user on multiple In-Place Holds for different cases or investigations


When you put a mailbox on In-Place Hold or Litigation Hold, the hold is placed on both the primary and the archive mailbox.

For more information, see In-Place Hold and Litigation Hold.

In-Place eDiscovery

Exchange Online lets customers search the contents of mailboxes across an organization using a web-based interface. Administrators or compliance and security officials who are authorized to perform In-Place eDiscovery search (by assigning) can search email messages, attachments, calendar appointments, tasks, contacts, and other items. In-Place eDiscovery can search simultaneously across primary mailboxes and archives. Rich filtering capabilities include sender, receiver, message type, sent/receive date, and carbon copy/blind carbon copy, along with KQL Syntax. Search results will also include items in the Deleted Items folder if they match the search query.

Results of In-Place eDiscovery searches can be previewed in the web-based interface, exported to a PST file or copied to a special type of mailbox called a Discovery mailbox. A Discovery mailbox has a 50 GB quota for storing search results. Administrators can also connect Outlook to the Discovery mailbox to access search results, and export the search results to a .pst file.

Administrators use either the Exchange admin center or remote Windows PowerShell to perform multi-mailbox searches. The Exchange admin center can provide a read-only preview of the search results, enabling administrators to quickly verify a search and rerun it, if needed, with different parameters. Once a search is optimized, the administrator can copy the results to the Discovery mailbox.

By default, one Discovery mailbox is created for each organization, but administrators can create additional Discovery mailboxes using remote Windows PowerShell. Discovery mailboxes cannot be used for any purpose other than storing In-Place eDiscovery search results.

Administrators use either the Exchange admin center or remote Windows PowerShell to perform In-Place eDiscovery searches. The Exchange admin center can provide a read-only preview of the search results, enabling administrators to quickly verify a search and rerun it, if needed, with different parameters. Once a search is optimized, the administrator can copy the results to the Discovery mailbox or export search results to a PST file.

Administrators can use either the Exchange admin center or remote Windows PowerShell to search up to 10,000 mailboxes at a time in an In-Place eDiscovery search.

In Exchange Online, authorized users can perform In-Place eDiscovery and choose one of the following actions:

  • Estimate search results Get an estimate of the number of messages the search will return, including keywords statistics to determine the effectiveness of keywords used in the search and tweak search parameters if required.

  • Preview search results

  • Copy messages returned in search results to a Discovery mailbox.

For more information, see In-Place eDiscovery.

Mail flow rules

You can use mail flow rules to look for specific conditions on messages that pass through your organization and act on them. Mail flow rules let you apply messaging policies to email messages, secure messages, protect messaging systems, and prevent information leakage.

Many organizations today are required by law, regulatory requirements, or company policies to apply messaging policies that limit the interaction between recipients and senders, both inside and outside the organization. In addition to limiting interactions among individuals, departmental groups inside the organization, and entities outside the organization, some organizations are also subject to the following messaging policy requirements:

  • Preventing inappropriate content from entering or leaving the organization

  • Filtering confidential organization information

  • Tracking or copying messages that are sent to or received from specific individuals

  • Redirecting inbound and outbound messages for inspection before delivery

  • Applying disclaimers to messages as they pass through the organization


Attachment file types that require installation of third-party iFilters on the email server (such as Adobe .pdf) cannot be inspected using mail flow rules until after an appropriate iFilter is installed. For more information about file types that are supported by mail flow rules, see Use mail flow rules to inspect message attachments in Office 365.

For more information about mail flow rules, see Mail flow rules in Exchange 2016.

Data loss prevention

The data loss prevention (DLP) feature will help you identify, monitor, and protect sensitive information in your organization through deep content analysis. DLP is a premium feature that is increasingly important for enterprise message systems because business-critical email includes sensitive data that needs to be protected. The DLP feature in Exchange Online lets you protect sensitive data without affecting worker productivity.

You can configure DLP policies in the Exchange admin center (EAC) management interface, which allows you to:

  • Start with a pre-configured policy template that can help you detect specific types of sensitive information such as PCI-DSS data, Gramm-Leach-Bliley act data, or even locale-specific personally identifiable information (PII).

  • Use the full power of existing transport rule criteria and actions and add new transport rules.

  • Test the effectiveness of your DLP policies before fully enforcing them.

  • Incorporate your own custom DLP policy templates and sensitive information types.

  • Detect sensitive information in message attachments, body text, or subject lines and adjust the confidence level at which Exchange Online acts.

  • Detect sensitive form data by using Document Fingerprinting. Document Fingerprinting helps you easily create custom sensitive information types based on text-based forms that you can use to define transport rules and DLP policies.

  • Add Policy Tips, which can help reduce data loss by displaying a notice to your Outlook 2016, Outlook 2013, Outlook on the web, and OWA for Devices users and can also improve the effectiveness of your policies by allowing false-positive reporting.

  • Review incident data in DLP reports or add your own specific reports by using a generate incident report action.

For more information about DLP, see Data Loss Prevention.


You can configure Exchange Online to journal copies of emails to any external mailbox that can receive messages via SMTP. Journaling can help your organization respond to legal, regulatory, and organizational compliance requirements by recording inbound and outbound email communications. When planning for messaging retention and compliance, it's important to understand journaling and how it fits in with your organization's compliance policies.

You can manage journal rules by using the Exchange admin center or remote Windows PowerShell. You can configure journaling on a per-user and per-distribution list basis, and choose to journal only internal messages, only external messages, or both. Journaled messages include not only the original message but also information about the sender, recipients, copies, and blind copies.

To ensure a successful and reliable journaling solution, you need to complete the following tasks:

  • Make sure that the journaling destination is not be an Exchange Online mailbox.

  • Create in the customer directory a contact object for the SMTP target email address to be used for journaling.

  • Create a second contact object as an alternative journal mailbox to capture any journal reports when the primary journal mailbox is unavailable.

  • Maintain proper management, redundancy, availability, performance, and functionality levels of the SMTP target to ensure successful mail acceptance always.

  • Provide respective interoperability with Exchange Server and Exchange transport including message formats, sender/recipient information integration, and appropriate content conversion.

For more information about journaling, see Journaling.

Feature availability

To view feature availability across plans, standalone options, and on-premises solutions, see Exchange Online service description.