In early December (2016) Microsoft announced that the default mailbox limits in Exchange Online would be raised to 100 GB, a massive increase from the 5 GB that we considered to be huge in the BPOS era. Who needs such a large mailbox? Well, we do now apparently.
While discussing this with my peers last week we noticed that most of us did not saw the change reflected in their tenants. Today I checked it again and saw that the new limits were applied to my mailboxes.
Note that the limits only change for mailboxes where the default limits were not updated. If you have set one of the three values to a non-default value, no changes were made automatically. Admins are able to change the values manually up to 100 GB.
Another thing to be aware of is that the new limits only apply to Exchange Online licenses that are purchased as part of an E3 or E5 subscription. If you’re purchasing Exchange Online as a separate SKU the old limit of 50 GB remains unchanged, the same applies for shared and resource mailboxes. For more information, see the Mailbox storage limits section in the Exchange Online Limits document on TechNet.