The largest attachment that can be attached to an email is 50 MB.
Please Note: Though we permit these large attachments, it is not guaranteed that the recipients will be able to receive it. A good rule of thumb, is if you are sending an attachment outside of the network, you should try not to go over 10 MB, as this is the average limit for many mailboxes.
Macintosh Users Please note: That the iMail application attachment size limit is standard at 25mb. For larger attachments we recommend using your Outlook Web App login.