Exchange Online (EXO) Email new Rate Limit Policy for HKU members

Exchange Online (EXO) Email new Rate Limit Policy for HKU members
  1. Microsoft announcement: Exchange Online no longer supports bulk or high-volume transactional email.
  2. Policy: Exchange Online will begin enforcing two limits for all cloud-hosted mailboxes, affecting all HKU member’s account:
    1. Recipient Rate limit (for both internal & external recipients) of 10,000 recipients in 24 hours.
    2. External Recipient Rate limit of 2000 recipients will be applied in 24 hours.

      The following is the deployment schedule:
      –Apr 2026 – Effective for all the existing HKU mailboxes accounts.
  3. What will be the impact?
    • Your HKU Exchange Online mailbox account will be limited to only delivering maximum 10,000 total recipients per day (in a 24-hour window), no matter if you are sending to internal recipients or external recipients.
    • In addition, your Exchange Online mailbox account will be also limited to only delivering maximum 2,000 external recipients per day, and it is a sub-limit of 10,000 recipients limit per day (in a 24-hour window).
    • Remember that if you are sending an Email to another Email domain within HKU, e.g. staff account (@hku.hk domain) sending Email to student account (@connect.hku.hk) will be considered as sending to external recipients, and vice versa.
    You can refer to the related knowledge base at here.
  4. What’s the workaround?
    1. For Internal communications to only HKU members recipients:
      • eNotices system (CF25) for information announcement at HKU portal (Most Recommended way)
      • Automatic Mailing List (AML) (CF49) to generate default mailing list for faculties or departments member
      • Exchange distribution list (CF158) generate customizable email group, e.g., group-<dept_abbre>-<group_name>
    2. External (or mixed Internal/External) communications:
      • Campus SMTP servers, please send enquiry to ithelp@hku.hk for suggestion of suitable mail server according to your provided information about number of recipient and mail content.
      • Mailman mailing-lists (application via CF48)
      • External contractor or custom-built mail applications

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