Skip to main content

Cornell University

Microsoft Outlook

On This Page

Microsoft Outlook is the university's default email system for faculty, staff, and affiliates. It is a cloud-based service that manages email, calendars, task lists, and address books.

Students: you are initially set up with Gmail to access email. You have the option to use Outlook instead. Read why you might want to consider doing so.

Accessing Email

Important Size Limits

These limits vary based on many factors. The numbers below reflect what most individuals will need, using Outlook on the Web and day-to-day email use. 

  • Mailbox size 50 GB.
  • Message size limit 112 MB (total size including attachments). The limit applies for both outgoing and incoming messages. See Attachments Not Getting Through for details.
  • Maximum number of attachments on a single message 250.
  • Maximum number of recipients per meeting invite and cancellations 2,500 per day.
  • Maximum subject length 255 characters.
If you need to send files larger than 25 MB, use Cornell Box (cloud storage that you can share) or Cornell Secure File Transfer instead (for sizes up to 5 GB)

Limits on Sending Very Large Mailings

Microsoft 365 includes some security defenses that limit the ability of an individual to send huge numbers of messages in a short amount of time. If you have legitimate large mailings to do, please understand these limits and the alternatives you have for delivering your messages.

  • Maximum number of addresses allowed in the To, Cc, and Bcc fields (combined): 500 per message
  • Maximum number of messages that can be sent from your email client per minute: 30
  • Maximum number of recipients who can receive messages sent from your account (or a Resource Account) in a 24-hour period: 10,000 (and no more than 5,000 can be to external addresses (that is, addresses other than


  • The 24-hour period is a rolling window: for example, if you send messages to 2,000 recipients at 8:30am, then messages to 5,000 recipients at 12 noon, then messages to 2,000 recipients at 2:30pm, and messages to 1,000 recipients at 4pm, you won't be able to send any more messages until 8:30am the next day.
  • If you try to send a message after exceeding the limit, you will either see an immediate error about the recipient limit, or the message will be returned to you with an error. Save the message to your Drafts folder and try again later.
  • A message will only be delivered if it can be delivered to all the recipients without going over the 10,000 limit. For example, if you've already sent messages to 9,900 recipients, and you attempt to send one message to 150 recipients, the second message will not be delivered because it would be 50 recipients over your limit for the 24-hour period.

Alternatives for Very Large Mailings

Support Contact:

Cornell IT Service Desk

Normal Business Hours: Monday-Friday, 8am-6pm (Eastern Time)
Emergency Service Disruptions: After Hours Support

Service Details:


As part of the Microsoft 365 suite of programs, Outlook provides email and calendaring services for the Cornell community.


To share feedback about this page or request support, log in with your NetID

At Cornell we value your privacy. To view
our university's privacy practices, including
information use and third parties, visit University Privacy.