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Cornell University

Email Delays and Order of Receipt

Email delivery times are usually a minute or less. At peak times, traffic can clog the tubes and cause delays.

This article applies to: Email @ Cornell

Over a half million messages are sent to and through the Cornell email system every day. That system includes Office 365, G Suite, and Lyris for e-lists. In addition, email often originates outside of Cornell's system, or is routed outside of our system for final delivery.

Microsoft documents a service target for Office 365 of delivering 95% of the email they receive within one minute of arrival at their system. Historically, Cornell has far exceeded that 95% level within the campus routing systems. E-lists can have more variability in delivery times because of queuing within the e-list system designed to protect other email systems from overwhelming blasts of mail from big lists.

If you receive an email that has taken much longer than, say, 30 minutes, to be delivered, you can check for the source of the delay by examining the message headers. See our View Full Headers article for the procedure for viewing headers in each email client. If you paste the message headers into a third-party utility, the Email Header Analyzer, you'll see a graphical display of the time spent in every stage of delivery.

If you're the sender of the message and want to know why its delivery was delayed, you'll need to ask the recipient to send you the full headers to investigate.

If delays are excessive in length or frequency, you can open a case with the IT Service Desk. Full message headers are required to investigate delays. 

CIT will inform you whether the delay was due to a known problem, service congestion, or other cause. Unless the cloud vendor does not meet their Service Level Agreement, there is little recourse beyond reporting the problem to them.

An additional factor that can cause messages to appear "out of sequence" in your Inbox is the geographical distribution of Office 365. Cornell mailboxes are distributed over four different data centers in the United States. For example,

  • Joe sends a message to Fred and Sally.
  • Sally's mailbox is in a data center that is experiencing heavy load, so the message to Sally is delayed.
  • However, Fred (through a different data center) receives the email right away and replies to all. 
  • The reply may take a different "highway" going to Sally, who then receives the reply a noticeable amount of time before she receives the original message.


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