Below are some of the limits for Microsoft 365 accounts - more detailed information can be found at Exchange Online Limits  

Starting Monday, February 5, 2018, both Microsoft 365 and UI Healthcare email systems increased the maximum message send/receive limits to 150mb.  This change is being made to allow easier collaboration within the University of Iowa.   Please keep the following in mind:

  • Maximum total message send/receive size is 150mb. This includes both the message content and attachments.
  • Attaching a large file to an email message requires uploading that file to the email system. This can increase the time required to send the message.
  • Email attachments count against overall email storage quota.
  • While the UI email systems allow sending and receiving 150mb email messages (including attachments), other external email systems continue to have smaller limits. Some common receiving limits are:
    • Gmail – 50mb
    • – 50mb
    • Yahoo – 25mb
    • Peer universities – varies
  • Whenever possible, it is advised to use a file collaboration tool for large files. The University of Iowa supports Microsoft OneDrive for Business which allows for file sizes larger than 150mb.
(Outlook on the web)
Outlook for iOS and Android Encrypted Messages
Message send/receive size limit (including attachments) -  Keep in mind that someone's mailbox on the Microsoft 365 server will be prohibited from receiving messages if they exceed their maximum quota limit.   Note:  when you attach a file to a message, the file size of the attachment increases (it can increase as much as 30% in size when it is sent).   Microsoft Message Limits 150 MB 112 MB 150 MB 33 MB 25 MB
Address List Limit 1000 1000 1000 1000 1000
Storage - User Mailbox, Shared Mailbox, Resource Mailbox 100 GB 100 GB 100 GB 100 GB 100 GB
Recipient Limit per message 300 300 300 300 300

NOTE:  Microsoft has implemented Receiving and Sending Limits.  They have stated that Microsoft 365 is not meant to be a bulk email service. "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." 


Quota Alerts Across Office 365:

Warning: 99GB 

Prohibit Send: 99.5 GB 

Prohibit Send/Receive: 100 GB

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Last updated: 
September 19, 2023