iSpeed Knowledge Base

Refer: https://technet.microsoft.com/en-us/library/exchange-online-limits.aspx

Receiving and sending limits

Receiving and sending limits are applied to combat spam and mass-mailing worms or viruses. These limits help to protect the health of our systems and keep our users safe.

Receiving limits

Receiving limits apply to the number of messages that a user, group, or public folder can receive per hour. This applies for both messages received from the Internet and from on-premises servers. When the receiving limit has been exceeded, any emails sent to that mailbox will receive a non-delivery report stating that the mailbox has exceeded the maximum delivery threshold. After one hour, the limit will refresh and the mailbox will once again be able to receive messages.

Sending limits

Sending limits apply to the number of recipients, number of messages, and number of recipients per message that a user can send from their Exchange Online account.

Note:
For distribution groups stored in an organization's address book, the group is counted as one recipient. For distribution groups stored in the Contacts folder of a mailbox, the members of the group are counted individually.

• Recipient rate limit   To discourage the delivery of unsolicited bulk messages, Exchange Online has recipient limits that prevent users and applications from sending large volumes of email. These limits are applied per-user to all outbound and internal messages.

  
  

  
  

  Note:
  Exchange Online customers who need to send legitimate bulk commercial email (for example, customer newsletters) should use third-party providers that specialize in these services.

  
  

  
  

• Recipient limit   This is the maximum number of recipients allowed in the To:, Cc:, and Bcc: fields for a single email message.

  
  

  
  

  Note:
  For the purposes of the recipient rate limit and the recipient limit, a distribution group that is stored in the organization's shared address book counts as one recipient. In a personal distribution list, each recipient is counted separately.

  
  

  
  

• Message rate limit   Message rate limits determine how many messages a user can send from their Exchange Online account within a specified period of time. This limit helps prevent overconsumption of system resources by a single sender. If a user submits messages at a rate that exceeds the limit via SMTP client submission, the messages will be rejected and the client will need to retry.

Sending limits across Office 365 options

Storage limits across Office 365 options

Note:

1 Each user initially receives 100 GB of storage in the archive mailbox. When auto-expanding archiving is turned on, additional storage is automatically added when the 100 GB storage capacity is reached. For more information, see Overview of unlimited archiving in Office 365. See the Office 365 Roadmap for details about availability. 2 To access a shared mailbox, a user must have an Exchange Online license. Shared mailboxes don’t require a separate license. However, if you want to enable In-Place Archive or put an In-Place Hold or a Litigation Hold on a shared mailbox, then an Exchange Online Plan 2 license or an Exchange Online Plan 1 with Exchange Online Archiving license is required. If you enable In-Place Archive and auto-expanding archiving for a shared mailbox, additional storage is automatically added when the 100 GB storage capacity for the archive mailbox is reached. 3 Resource mailboxes don’t require a license. 4 In-Place Archive isn’t included in Exchange Online Kiosk. However, it can be purchased as an add-on through Exchange Online Archiving. For more information, please see the Exchange Online Archiving Service Description. 5 Site mailboxes are created and managed in SharePoint Online. For more information, see Prepare for using site mailboxes in Office 365. 6 You are limited to 1000 public folder mailboxes, and the maximum total size of all public folder mailboxes is 50 TB. 7 In-Place Archive can only be used to archive mail for a single user or entity (such as a shared mailbox) for which a license has been applied. Using an In-Place Archive as a means of storing mail from multiple users or entities is prohibited. For example, an IT administrator can’t create a shared mailbox and have users copy it (through the Cc or Bcc field, or through a transport rule) for the explicit purpose of archiving. Note that a shared mailbox that multiple people use does not actually store email for those individual users. Multiple users have access, and they send email as the shared mailbox. Therefore, the only emails stored in the shared mailbox are those sent to or from it, as the shared mailbox. 8 If you have created a retention policy in Exchange Online, messages will be automatically moved to a user’s archive mailbox only if the user’s primary mailbox is larger than 10 MB. The retention policy will not run automatically for mailboxes that are smaller than 10 MB.

Message limits

The following limits are applied to every email message.

• Message size limit   Message size limits are necessary to prevent large messages from blocking delivery of other messages and affecting service performance for all users. These limits include attachments, and apply organization-wide to all messages (inbound, outbound, and internal). Messages larger than this limit will not be delivered, and the sender will receive a non-delivery report (NDR). While message size limits can be configured up, down, or on a per-user basis, administrators can also create transport rules to limit the maximum size of any individual attachment. To learn more, see Office 365 now supports larger email messages.

  
  

  
  

  Note:
  Particular email clients may have lower message size limits or may limit the size of an individual file attachment to a value that is less than the Exchange Online message size limit.

  
  

  
  

• Subject length limit   The maximum number of text characters allowed in the subject line of an email message.

• File attachments limit   The maximum number of file attachments allowed in an email message. Even if the total size of all the file attachments doesn't violate the message size limit, there is still a limit on how many attachments are allowed in the message. This limit is controlled by the multipart message limit.

• File attachment size limit   The maximum file size of a single attachment.

  
  

  
  

  Note:
  This is the maximum file size of a single attachment. Individual client programs, including Outlook Web App, may limit the size of attachments below this maximum. Exchange ActiveSync does not implement attachment size limits on an individual attachment basis. The total size of all attachments to an Exchange ActiveSync message must be less than the message size limit.

  
  

  
  

• Multipart message limit   The maximum number of message body parts that are allowed in a MIME multipart message. This limit also controls the maximum number of file attachments that are allowed in a message.

• Embedded message depth limit   The maximum number of forwarded email messages that are allowed in an email message.

Message limits across Office 365 options

Note:

1 Office 365 Administrators can specify a custom limit between 1 MB and 150 MB. However, the size of message you can send or receive also depends on what your email client or solution supports. For more information about customizing the maximum allowed message size for your organization, see Office 365 now supports larger email messages. 2 You can send and receive up to 150 MB messages between Office 365 users (where the message never leaves the Office 365 datacenters). Messages that are routed outside of the Office 365 datacenters are subject to an additional 33% translation encoding increase, in which case the maximum message size is 112 MB. 3 OWA accounts for the possibility that your message may be subject to the 33% encoding increase and restricts the size of message you can send to 25% less than the configured setting. For example, if you customize your settings for a 100 MB maximum message size, you can send messages no larger than 75 MB. 4 The size of messages to be moved into Exchange Online are computed by Exchange Online. Versions of Exchange prior to Exchange Server 2013 may report a smaller item size. This limit applies to move based migrations using any supported Exchange Mailbox Replication Service. Other migration methods (Cutover, Staged, IMAP, PST) and other third party tools are limited by the general message size limit. 5 For information about OME with new capabilities, see Set up new Office 365 Message Encryption capabilities built on top of Azure Information Protection.