Microsoft Exchange Online is a hosted email, calendar, contacts and tasks solution that delivers the capabilities of Microsoft Exchange Server as a cloud-based service. Exchange Online is essentially based on Microsoft Exchange Server, hence it supports most if not all features of on-premise Exchange Server including full integration with Active Directory, group policy support, and familiar messaging experience across various forms of PCs, computers, Web, smartphones and mobile devices.

Exchange Online is one of the product under the umbrella of Office 365, and it’s included in many Office 365 plans that include email service. Exchange Online is also available for subscription on a standalone basis for users who just need a hosted Exchange service without other unnecessary add-ons.

As a standalone SKU, Exchange Online has three plans available, namely Exchange Online Plan 1, Exchange Online Plan 2 and Exchange Online Kiosk. All Exchange Online plans can have unlimited number of users. The table below describes the differences and comparison between features and functionality available in each different plans.

Exchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Office 365 SKUs & Plans InclusionOffice 365 Business Essentials
Office 365 Business Premium
Office 365 Enterprise E1
Office 365 Education E1
Office 365 Government E1
Office 365 Enterprise E3
Office 365 Education E3
Office 365 Government E3
Office 365 Enterprise E4
Office 365 Education E4
Office 365 Government E4
Office 365 Enterprise K1
Office 365 Government K1
FeatureExchange Online Plans
Planning and DeploymentExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Hybrid deployment supportedYesYesYes
IMAP migration supportedYesYesYes
Cutover migration supportedYesYesYes
Staged migration supportedYesYesYes
PermissionsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Role-Based PermissionsYesYesNo
Role GroupsYesYesNo
Role Assignment PoliciesYesYesNo
Message Policy and ComplianceExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Archiving Exchange Online-based MailboxesYesYesNo
Cloud-Based Archiving of On-Premises MailboxesNoNoNo
Retention Tags and Retention PoliciesYesYesYes
Encryption of data at rest (BitLocker)YesYesYes
IRM using Azure RMS (requires add-on purchase, included in E3 & E4)NoNoNo
IRM using Windows Server AD RMSYesYesYes
Office 365 Message Encryption (depends on Azure RMS)NoNoNo
S/MIMEYesYesYes
In-Place Hold and Litigation HoldNoYesNo
In-Place eDiscoveryYesYesYes
Transport RulesYesYesYes
Data Loss PreventionNoYesNo
JournalingYesYesYes
Anti-Spam and Anti-Malware ProtectionExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Built-In Anti-Spam ProtectionYesYesYes
Customize Anti-Spam PoliciesYesYesYes
Built-In Anti-Malware ProtectionYesYesYes
Customize Anti-Malware PoliciesYesYesYes
Quarantine – administrator managementYesYesYes
Quarantine – end-user self-managementYesYesYes
Mail FlowExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Custom Routing of Outbound MailYesYesYes
Secure Messaging with a Trusted PartnerYesYesYes
Conditional Mail RoutingYesYesYes
Adding a Partner to an Inbound Safe ListYesYesYes
Hybrid Email RoutingYesYesYes
RecipientsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Capacity AlertsYesYesYes
ClutterYesYesYes
MailTipsYesYesYes
Delegate AccessYesYesNo
Inbox RulesYesYesNo
Connected AccountsYesYesYes
Inactive MailboxesNoYesNo
Offline Address BookYesYesYes
Address Book PoliciesYesYesYes
Hierarchical Address BookYesYesNo
Address Lists and Global Address ListYesYesYes
Distribution GroupsYesYesYes
External Contacts (global)YesYesYes
Universal Contact CardYesYesYes
Contact Linking with Social NetworksYesYesYes
Resource MailboxesYesYesYes
Conference Room ManagementYesYesYes
Out-of-Office RepliesYesYesYes
Calendar SharingYesYesYes
Reporting Features and Troubleshooting ToolsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Office 365 admin center reportsYesYesYes
Excel Reporting WorkbookYesYesYes
Web Services ReportsYesYesYes
Message TraceYesYesYes
Auditing ReportsYesYesYes
Unified Messaging ReportsNoYesNo
Sharing and CollaborationExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Federated SharingYesYesYes
Site Mailboxes (requires SharePoint Online)YesYesYes
Public FoldersYesYesNo
Clients and Mobile DevicesExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Microsoft OutlookYesYesNo
Outlook Web AppYesYesYes
Exchange ActiveSyncYesYesYes
POP and IMAPYesYesYes (no IMAP)
SMTPYesYesYes
EWS Application supportYesYesNo
Outlook for MacYesYesNo
Voice Message ServicesExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Voice MailNoYesNo
Third-Party Voice Mail InteroperabilityYesYesYes
Skype for Business IntegrationYesYesYes
High Availability and Business ContinuityExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Mailbox Replication at Data CentersYesYesYes
Deleted Mailbox RecoveryYesYesYes
Deleted Item RecoveryYesYesYes
Single Item RecoveryYesYesNo
Interoperability, Connectivity, and CompatibilityExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Skype for Business Presence in OWAYesYesNo
SharePoint InteroperabilityYesYesYes
EWS Connectivity SupportYesYesYes
SMTP Relay SupportYesYesYes
Exchange Online Administration and ManagementExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Microsoft Office 365 portal accessYesYesYes
Microsoft Office 365 admin center accessYesYesNo
Exchange admin center accessYesYesYes
Remote Windows PowerShell accessYesYesYes
ActiveSync Policies for Mobile DevicesYesYesYes
Usage ReportingYesYesYes
Customization, Add-ins, and Resources for Exchange OnlineExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Outlook Web App Web PartsYesYesYes
Outlook Add-Ins and Outlook MAPIYesYesNo
LimitsExchange Online Plans
Address Book LimitsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Address List100010001000
Offline Address Book (OAB)250250250
Address Book Policies (ABP)250250250
Global Address Lists250250250
Storage LimitsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
User Mailboxes50 GB50 GB2 GB
Archive MailboxesShared with PrimaryNo LimitNot Available
Shared Mailboxes50 GB50 GBNot Available
Resource Mailboxes50 GB50 GB50 GB
Public Folder Mailboxes (Max 50)50 GB50 GBNot Available
Mailbox Folder LimitsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Maximum number of messages per mailbox folder1 million1 million1 million
Maximum number of messages per folder in the Recoverable Items folder3 million3 million3 million
Maximum number of subfolders per mailbox folder1,0001,0001,000
Maximum folder hierarchy depth300300300
Maximum number of public folders100,000100,000Not Available
Maximum number of subfolders per public folder1,0001,000Not Available
Storage LimitsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
User Mailboxes50 GB50 GB2 GB
Archive MailboxesShared with PrimaryNo LimitNot Available
Shared Mailboxes50 GB50 GBNot Available
Resource Mailboxes50 GB50 GB50 GB
Public Folder Mailboxes (Max 50)50 GB50 GBNot Available
Message LimitsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Message size limit25 MB25 MB25 MB
Message size limit – migration150 MB150 MB150 MB
Subject length limit255 characters255 characters255 characters
File attachments limit250 attachments250 attachments250 attachments
File attachment size limit25 MB25 MB25 MB
Multipart message limit250 parts250 parts250 parts
Embedded message depth limit30 embedded messages30 embedded messages30 embedded messages
Recipient and Sender LimitsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Recipient rate limit10,000 recipients per day10,000 recipients per day10,000 recipients per day
Recipient limit500 recipients500 recipients500 recipients
Distribution Group LimitsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Maximum number of distribution group members100,000 members100,000 members100,000 members
Limit sending messages to large distribution group5,000 or more members5,000 or more members5,000 or more members
Maximum message size for large distribution groups2 MB2 MB2 MB
Transport and Inbox Rule LimitsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Maximum number of transport rules300 rules300 rules300 rules
Maximum size of an individual transport rule8 KB8 KB8 KB
Character limit (in KB) for all regular expressions used in all transport rules20 KB20 KB20 KB
Maximum number of recipients added to a message by all transport rules100 recipients100 recipients100 recipients
Forwardee limit10 recipients10 recipients10 recipients
Number of times a message is redirected1 redirection1 redirection1 redirection
Moderation LimitsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Maximum size of the arbitration mailbox10 GB10 GB10 GB
Maximum number of moderators10 moderators10 moderators10 moderators
Expiration for messages waiting for moderation2 days2 days2 days
Maximum rate for expired moderation notification messages300 expiration notifications per hour300 expiration notifications per hour300 expiration notifications per hour
Exchange ActiveSync LimitsExchange Online Plan 1Exchange Online Plan 2Exchange Online Kiosk
Exchange ActiveSync device limit100100100
Exchange ActiveSync device deletion limit202020
Exchange ActiveSync file attachment limit25 MB25 MB25 MB

Source: TechNet