This topic describes recipient-related features included with Microsoft Exchange Online. This includes email, contacts, distribution groups, and calendar and scheduling capabilities.


Every Microsoft Exchange Online subscriber receives a mailbox, and specialty mailboxes are available for scheduling facilities resources (such as conference rooms) and for multiuser access to shared email addresses. Maximum storage limits apply to most mailboxes, and administrators can control allowable mailbox sizes. Automated notifications and restrictions can alert users when their mailboxes are nearing, or at, capacity. Exchange Online also has several types of message limitations—message size, message rate, and recipient list limits. Details of all these features and limits are provided below.


Catch-all addresses are no longer supported in Exchange Online. Due to recipient filtering in place to protect against potential spam messages, email addresses that do not exist in your Office 365 tenant will be rejected.

Mailbox types, storage limits, and capacity alerts

The amount of mailbox storage available to a user and the default mailbox size are determined by the mailbox type and the user's subscription license. Administrators can reduce maximum mailbox sizes per user or globally. Exchange Online also provides notifications when a user's mailbox is nearing, or at, capacity.

For more information, see the "Mailbox storage limits" and "Capacity alerts" sections in the topic, Exchange Online Limits.


MailTips are automated, informative messages that appear above the To: line while users are composing or addressing a message. They are designed to help prevent accidental delivery, policy violations, or unnecessary non-delivery reports (NDRs). For example, MailTips can generate an alert if senders try to send messages to overly large groups, to groups that contain external recipients, or to a distribution group that is moderated or restricted. For more information, see MailTips.

Delegate access

Exchange Online supports delegate access—the ability for users to allow others to manage their email and calendars. Delegate access is commonly used between a manager and an assistant, where the assistant processes the manager's incoming email messages and coordinates the manager's schedule. Delegate access can be enabled by Exchange Online users in Outlook or Outlook Web App, or by administrators in the Exchange Admin Center.

Delegates can have two types of access:

  • Send on Behalf permissions The delegate can compose email messages and enter the other person's name in the From field, where it will be displayed as "[delegate name] on behalf of [person's name]."

  • Send As permissions The delegate can send messages from the other person's mailbox as if the delegate were the mailbox owner. This scenario is common where there is a shared mailbox and several employees send email messages from that shared mailbox instead of from their Exchange Online accounts.

For more information about delegating access, see Manage Permissions for Recipients.

Inbox rules

Exchange Online allows users to create inbox rules that automatically perform specific, criteria-based actions on messages as they arrive. For example, they can create a rule to automatically move all mail to a specific folder if the mail was sent to a certain distribution group. Users manage inbox rules from Outlook or Outlook Web App. Administrators can block certain types of inbox rules by disabling server-side forwarding and/or server-side automatic replies. For example, disabling server-side email forwarding can prevent users from automatically forwarding email to personal accounts. Similarly, disabling server-side automatic replies can prevent outside parties from using these replies to identify valid email addresses. These changes are made through remote Windows PowerShell.


Clutter is designed to help you focus on the most important messages in your inbox. It uses machine learning to de-clutter your inbox by moving lower priority messages out of your way and into a new Clutter folder. Clutter respects your existing email rules, so if you have created rules to organize your email those rules continue to be applied and Clutter won't act on those messages. Clutter is disabled by default for your inbox. To learn more, see De-clutter your inbox in Office 365.

Connected accounts

The Connected Accounts feature enables Exchange Online users to connect external email accounts (such as personal accounts) to their internal email accounts in Exchange Online, and then use Outlook Web App to interact with all their messages in one place. Connected Accounts automatically synchronize upon sign-in to Outlook Web App; users can also manually synchronize the accounts from Outlook Web App. Administrators can enable and disable this feature for specific users or all users through the Exchange admin center.

Inactive mailboxes

Exchange Online provides the capability to preserve the contents of deleted mailboxes indefinitely. This feature is called inactive mailboxes. A mailbox becomes inactive when an In-Place Hold or a Litigation Hold is placed on the mailbox before it's deleted. This results in the contents of the mailbox being preserved indefinitely. Administrators, compliance officers, or record managers can use the In-Place eDiscovery feature in Exchange Online to access the contents of an inactive mailbox.

Enabling an inactive mailbox requires that the mailbox is assigned an Exchange Online (Plan 2) license or has an Exchange Online Archiving subscription so that an In-Place Hold or a Litigation Hold can be placed on the mailbox before it's deleted.


If a hold isn't placed on a mailbox before it's deleted, the contents of the mailbox will not be preserved or discoverable. The mailbox can be recovered within 30 days of deletion, but the mailbox and its contents will be permanently deleted after 30 days if it isn't recovered.

For more information, see:

Contacts and distribution groups

Offline Address Book

The Offline Address Book feature provides a snapshot of the Active Directory information available in the Outlook Global Address List. It is cached locally in Outlook to make it available when a user is working offline.

Address Book Policies

Exchange Online supports Address Book Policies. Address Book Policies (ABPs) allow you to segment users into specific groups to provide customized views of your organization's global address list (GAL). When creating an ABP, you assign a GAL, an offline address book (OAB), a room list, and one or more address lists to the policy. You can then assign the ABP to mailbox users, providing them with access to a customized GAL in Outlook and Outlook Web App. Administrators can configure address book policies by using remote Windows PowerShell. To learn more about Address Book Policies, see Address Books in Exchange Online.

Address Lists

Exchange Online supports the customization of Address Lists and Global Address List, an organization-wide directory of all mail-enabled users, distribution groups, and external contacts. Administrators can hide users, distribution groups, and contacts from the Global Address List by using the Directory Synchronization tool or remote Windows PowerShell.

Hierarchical address books

Hierarchical address books allow end users to browse for recipients in their Exchange organization using an organizational hierarchy. Administrators can customize the address book by seniority and rank rather than alphabetical listings.

Distribution groups (global)

A distribution group (or distribution list) is a collection of users, contacts, and other distribution groups that are available to all users in a company. Users address email to a distribution group alias to send messages to all people in the group. Distribution groups are similar to personal distribution groups that individuals create in Outlook, only their member lists are globally available to the company. Administrators create distribution groups in the Exchange admin center. The groups can also be synchronized with Exchange Online from on-premises Active Directory. They appear in the Global Address List in Outlook. Exchange Online supports advanced distribution group capabilities, including these described below:

  • Restricted distribution groups By default, anyone can send emails to any distribution group. Administrators can change permissions to allow only specific individuals to send emails to a particular group—for example, to discourage inappropriate use of large distribution lists. Administrators can also block external sources from sending email to distribution groups to help prevent spam. For distribution groups that are synchronized from on-premises Active Directory using the Directory Synchronization tool, the attributes for restriction are synchronized to the cloud automatically. For more information, see Manage Distribution Groups.

  • Dynamic distribution groups The membership list for a dynamic distribution group (also known as a dynamic distribution list, or query-based distribution list) is calculated every time a message is sent to the group. This calculation is based on filters and conditions that the administrator defines. They are managed in Exchange Online through remote Windows PowerShell. For more information about dynamic distribution groups, see Manage Dynamic Distribution Groups.


    The Office 365 Directory Synchronization tool ignores dynamic distribution groups in on-premises Active Directory, and does not synchronize these to Exchange Online. Organizations that use the Directory Synchronization tool should use a naming convention that avoids conflicts between the regular distribution groups that are managed on-premises and the dynamic distribution groups that are managed in Exchange Online.

  • Moderated distribution groups Administrators can select a moderator to regulate the flow of messages to a distribution group. With moderated distribution groups, anyone can email the distribution group alias, but before the message is delivered to the members of the group, a moderator must review and approve it. For more information about moderation, see the Message Approval section in Manage Distribution Groups.

  • Self-Service distribution groups Administrators can give users the ability to manage their own distribution group membership from a web-based interface. Users can be given permissions to create, delete, join, or leave distribution groups. These capabilities are enabled by default for all Exchange Online users. Administrators can disable them so that only the IT department can manage distribution groups, if desired. They can also create naming policies to standardize and manage the names of distribution groups that their users create. For example, they can add a specific prefix or suffix to the distribution group name when it is created, or block specific words from being used in the group's name.


    Self-service capabilities are not available for distribution groups that are synchronized from on-premises Active Directory to Exchange Online. Organizations that use Directory Synchronization should use a naming convention that avoids conflicts between distribution groups that are managed on-premises and distribution groups that are managed in the cloud.

External contacts (global)

An external contact is a record with information about a person who works outside of a specified organization. External contacts are similar to personal contacts that individuals create in Outlook, only they are globally available to the company. Administrators create external contacts using the Exchange admin center or remote Windows PowerShell. These contacts can also be synchronized with Exchange Online from on-premises Active Directory. They appear in the Global Address List in Outlook.

For more information about external contacts, see Create an organization relationship in Exchange Online.

Calendar and scheduling

Resource mailboxes

Resource mailboxes (such as for conference rooms and physical equipment) represent a company's meeting rooms or other facilities or resources. Users can reserve rooms or resources by adding the resource's email alias to meeting requests in Outlook or Outlook Web App. Conference rooms and resources appear in the Global Address List in Outlook and Outlook Web App.

Administrators create resource mailboxes using the Exchange admin center or remote Windows PowerShell. The mailboxes can also be synchronized with Exchange Online from on-premises Active Directory.

For more information about resource mailboxes, see:

Conference room management

Exchange Online includes the Resource Booking Attendant (RBA), which automates scheduling of conference rooms and other resources. A resource mailbox that is RBA-configured accepts, declines, or acknowledges meeting requests from a meeting organizer based on the resource's calendar availability.

Administrators can customize automated conference room responses and configure booking policies in Outlook Web App. These policies include who can schedule the resource, when it can be scheduled, what meeting information is visible on the resource's calendar, and the percentage of scheduling conflicts allowed. Administrators can disable the Resource Booking Attendant and assign specific users to manually manage meeting requests for conference rooms.

Administrators must define and manage RBA settings through remote Windows PowerShell.

Out-of-office replies

Out-of-office messages are automatic replies to incoming messages that Exchange Online sends on behalf of a user. Users can schedule out-of-office messages in advance, with specific start and end times, and can configure separate out-of-office messages for internal and external recipients. They can also set out-of-office messages from mobile devices that support this Exchange ActiveSync feature. Junk-email and mailing-list awareness within Exchange Online prevents users from sending external out-of-office messages to extended mailing lists and potential spammers. Administrators can also prevent users from sending out-of-office messages to external users using remote Windows PowerShell.

Calendar sharing

Users can share their personal calendar in one of two ways:

  • Federated calendar sharing Federation refers to the underlying trust infrastructure that supports federated sharing, an easy method for Exchange users to share free/busy calendar data and contact information with recipients in other external federated organizations. These include Exchange Online organizations or organizations running Exchange Server 2010 or Exchange Server 2013 on-premises. Exchange Online administrators do not need to set up a trust with the Microsoft Federation Gateway because this trust is pre-configured for all Exchange Online customers when the Office 365 tenant service is created. A default sharing policy allows users to send calendar-sharing invitations from Outlook Web App or Outlook 2010. Administrators use remote Windows PowerShell to disable this policy or to configure the level of free/busy calendar data that users can share. Administrators can also create an organization-to-organization relationship with another federated org, which allows the desired level of free/busy information for every user to be visible cross-organization without the need for individual users to make a sharing invitation. Within the scope of administrator-defined Sharing Policies and/or organization-organization relationships, users can individually limit the detail of their sharing further.

  • Internet calendar sharing Exchange Online allows users to publish their calendars using the iCal format for anonymous access by anyone inside or outside the organization. Recipients can be using Exchange, another platform, or simply a web browser. Exchange Online users can also subscribe to calendars that others have published to Internet locations through iCal. This personal calendar sharing is different than federated calendar sharing, which is configured by an administrator and provides organization-to-organization free/busy sharing. No user can publish calendar data in iCal format until the administrator has set and applied a Sharing Policy that allows it. Administrators can disable iCal publishing and iCal subscriptions for users in an organization by using remote Windows PowerShell.

For more information about federated sharing, see Sharing in Exchange Online.

Outlook 2010 Room Finder

Exchange Online supports the Room Finder feature of Outlook 2010, which arranges rooms into lists (for example, a list called "Building 5 rooms") to make it easier to find a nearby room when scheduling a meeting. To appear in the room list, a distribution group must be specially marked using one of two methods:

  • A new room list can be created by using remote Windows PowerShell.

  • Any distribution group that contains only rooms can be converted to a room list through remote Windows PowerShell.

Feature Availability

To view feature availability across Office 365 plans, standalone options, and on-premise solutions, see Exchange Online Service Description.