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Roadmap Item Says Rollout to Start in October 2026
According to Microsoft 365 roadmap item 560820 (last updated on 2 September 2026) Microsoft plans to increase the expansion limit for auto-expanding archives past 1.5 TB next month, but only for users with Office 365 E5 or Microsoft 365 E5 licenses (“eligible E5 licenses”).
The History of Auto-Expanding Archives
It’s an interesting development that brings auto-expanding archives closer to the promise made in June 2015 when Microsoft announced “new auto-expanding, highly scalable archiving. This allows you to take advantage of a truly bottomless archive…” for Exchange Online customers with E3 or above licenses (Exchange Online Plan 2).
Microsoft started to deploy auto-expanding archives in early 2016 and updated the Exchange service description to say that archive mailboxes had “no limit.” Some people cheerfully filled their archives with information imported from third-party archive systems and rapidly expanded the archive mailboxes to occupy terabytes of data. Everything seemed to be going well.
And then some unforeseen technical problems came into play. The issues slowed deployment to a crawl and forced Microsoft to impose rules such a maximum expansion rate of 1/GB per day for archive mailboxes.
Exchange Online uses Database Availability Groups (DAGs) with mailbox databases deployed on JBOD storage. At the time, Microsoft used 8 TB drives because they were cheap and easily available. An 8 TB drive is great until you start to create logical archives composed of “chunks” or “shards” of storage that are stitched together to form an auto-expanding archive mailbox. Everything is fine as long as the archives remain small, but once they go over 5 TB or so, operational issues like being able to fit archive mailboxes into mailbox databases or being able to move mailboxes between databases to rebalance load compromised the ability of DAGs to maintain service to users.
Eventually, the issues stopped the notion of an endless archive dead in the water. After struggling with the operational issues for several years, Microsoft halted the endless nature of auto-expanding archive mailboxes and limited their capacity to 1 TB in November 2019, before increasing the limit to 1.5 TB in November 2021. The 1.5 TB limit is what we have today. My archive mailbox is a paltry 5.85 GB, so I have some room to expand (Figure 1).
Gaps in the Roadmap Item
Roadmap items are never as descriptive and insightful as Microsoft 365 message center notifications, which are published much closer to the actual availability of new capabilities. For example, we don’t know what limit will be placed for E5 mailboxes. We don’t know if larger archive mailboxes will be licensed through a service plan (I suspect that they will) that will also be available separately. We don’t know if Microsoft will deliver any new tools to help tenants manage massive archive mailboxes. In short, there’s a lot to discover about what roadmap item 560820 will deliver.
I’ve heard some speculation that Microsoft will sell additional archive space much like they sell extra SharePoint Online storage. Despite some reports suggesting consumption-based pricing, the roadmap item itself contains no mention of charges for additional archive capacity.
That being said, Microsoft could turn on a dime and change how it delivers larger archive mailboxes. I guess we’ll see.
A Capability for the Few, Not the Many
I don’t think the arrival of extra-large archive mailboxes will be something of consequence to many Microsoft 365 users. Preserving massive quantities of mailbox data is clearly important for some organizations, but for most tenants a 1.5 TB archive mailbox is already far larger than anything they are likely to need. For me, a 1.5 TB limit is just fine.
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