Last updated: 21 July 2026
Mailbox quotas by plan, what changed in mid-2026, and what it costs once a mailbox goes over the limit.
What changed
Microsoft increased the standard per-mailbox storage quota from 50GB to 100GB across Microsoft 365 Business plans, effective 1 July 2026. Enterprise plans have historically carried different baseline quotas than Business plans. Since Microsoft has changed these numbers before, always confirm the current figure for your specific tenant in the Microsoft 365 admin centre rather than relying on a fixed number from any one page.
Over the limit
A recurring monthly add-on, commonly around $0.20/GB/month, plus an auto-expanding archive option (up to 1.5TB) for larger overflow — a cost that compounds across every mailbox that needs it.
A one-off action with no recurring charge — for a mailbox with years of unread newsletters and old attachments, this usually resolves quota pressure without ever needing the paid add-on.
It depends on the plan, and it changed recently: Microsoft increased the standard per-mailbox quota from 50GB to 100GB across Microsoft 365 Business plans, effective 1 July 2026. Enterprise plans (E3/E5) have historically included larger baseline quotas than Business plans — always check the current admin centre for your specific tenant's exact figure, since Microsoft has changed these limits before and can again.
Microsoft sells extra storage as a paid add-on, commonly listed around $0.20/GB/month, though the exact rate isn't fixed globally and varies by region, currency, and agreement type. For larger overflow, Exchange Online Archiving offers an auto-expanding archive up to 1.5TB (a flat add-on fee, included on some higher plans), with anything beyond that billed per-GB as a consumption feature.
No — Microsoft's own documentation describes Outlook performance pauses appearing once a local data file (OST) passes around 10GB, increasing in frequency from 25GB, independent of the mailbox's actual storage quota. A mailbox well within its plan's limit can still be the one generating "Outlook is slow" tickets.
Buying more storage is a recurring monthly cost that compounds across every mailbox that needs it; cleaning up a mailbox is a one-off action with no ongoing charge. For a mailbox with years of unread newsletters and old attachments, cleanup usually resolves the immediate quota pressure without needing the add-on at all — see the full cost breakdown on the storage costs page.
Smart Sweep and Storage Cleanup let every employee clear their own mailbox — no per-mailbox IT time, no storage add-on invoice.