Mailbox storage limits


The amount of mailbox storage available is determined by the mailbox type and the user’s subscription license. Administrators can reduce maximum mailbox sizes per user or globally.





Message limits


The following limits are applied to every email message.


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.


Message size limit - Outlook: 150mb

Message size limit - OWA: 112mb

Message size limit - Outlook for Mac: 35mb


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 attachments limit: 250 attachments



File attachment size limit


The maximum file size of a single attachment.


File attachment size limit - Outlook: 150mb

File attachment size limit - OWA: 35mb

File attachment size limit - Outlook for Mac: 35mb