Microsoft Doubles Mailbox Storage to 100 GB for Microsoft 365 Business Users
Expanded mailbox capacity gives SMBs more room to manage growing email volumes without changing plans.
Key Takeaways:
- Microsoft 365 Business Basic, Standard, and Premium users are eligible for 100 GB mailboxes.
- The new entitlement combines the standard 50 GB mailbox with an additional 50 GB storage plan.
- Administrator-defined mailbox quotas remain unchanged during the rollout.
Microsoft is giving small and medium-sized businesses more room to manage growing email volumes by doubling the mailbox storage for eligible Microsoft 365 Business users from 50 GB to 100 GB. This change began rolling out in June as part of the 2026 Microsoft 365 packaging updates.
Specifically, Microsoft has recently updated mailbox storage entitlements for certain Microsoft 365 Business subscriptions, which increases the primary mailbox size available to eligible users to 100 GB. The additional storage changes will apply to customers with Microsoft 365 Business Basic, Business Standard, and Business Premium subscriptions.
What do administrators need to know about the storage upgrade?
The 100 GB mailbox entitlement is provided through two combined service plans within the Microsoft 365 Business suite. The first plan, BPOS_S_STANDARD, provides a base mailbox capacity of 50 GB, while the EXCHANGE_STORAGE_50GB service plan adds another 50 GB of storage. Users must have both service plans enabled under their assigned license to receive the full 100 GB mailbox quota.
“A user who has multiple licenses assigned, which contain multiple Exchange service plans (this is known as Concurrent Licensing), will be granted the maximum quota provided by a single product – the quotas are not additive across products. For example, a user with one of the Business Suite and a separate Enterprise license containing Exchange Online Plan 2, will still be entitled to 100 GB. The quota increase for the Business suites affects the base mailbox size only. It does not provide archive capabilities,” the Exchange team explained.
Custom mailbox quotas remain unchanged
Microsoft preserves any mailbox quotas that administrators have manually configured, which ensures that the additional 50 GB entitlement does not automatically override existing custom settings. Similarly, if the extra storage entitlement is later removed, any administrator-defined quota remains unchanged to help organizations maintain their intended mailbox management policies.
Microsoft says the gradual rollout of the packaging changes will continue through September 2026. The company has warned that administrators should not remove and reassign licenses to force a mailbox quota refresh, as doing so can disrupt service access and potentially trigger the applicable data-retention lifecycle.
Rabia has a master's degree in Software Engineering and she has years of experience writing professionally about Microsoft products and other technologies. Rabia has also written for OnMSFT.com as well as Windows Report. She is always up to date on t...
