Exchange Mailbox Limits – Export None Default Quotas to CSV

Exporting Mailboxes Without Default Quota Limits to CSV

In most Exchange organisations, mailbox size limits are set once at the database level and every mailbox inherits them by default — but it’s easy over time to end up with individual mailboxes that have had custom (or no) limits set directly on the mailbox, overriding the database default, sometimes without anyone remembering why. To find every mailbox that is not using the database’s default quota settings, run this from the Exchange Management Shell (EMS):

Get-Mailbox -ResultSize Unlimited | Where-Object {$_.UseDatabaseQuotaDefaults -eq $false} |
Select-Object DisplayName, UseDatabaseQuotaDefaults, IssueWarningQuota, ProhibitSendQuota, ProhibitSendReceiveQuota |
Export-Csv C:\Temp\CustomQuotaMailboxes.csv -NoTypeInformation

This gives you a clean CSV of exactly which mailboxes have a custom quota configuration, and what those custom limits are set to, which is a useful housekeeping check ahead of a storage review or before rolling out a new database-wide quota policy — you’ll want to know in advance which mailboxes will be unaffected by a database-level change because they already have their own explicit override.

This Doesn’t Apply the Same Way in Exchange Online (Updated for 2026)

This query is specifically for on-premises Exchange — the UseDatabaseQuotaDefaults property doesn’t carry over to Exchange Online, because EXO has no database-default-quota concept to override in the first place. In Exchange Online, mailbox size is tied to the assigned Microsoft 365/Exchange Online licence plan rather than a per-database setting, so there’s nothing equivalent to audit here. If you need to check or override an individual mailbox’s quotas in Exchange Online, the properties themselves (ProhibitSendQuota, ProhibitSendReceiveQuota, IssueWarningQuota) still exist and can still be set per-mailbox — just run Get-Mailbox <identity> | Select *Quota* against Exchange Online PowerShell to see them — there’s simply no “using the default vs. overridden” distinction to filter on, since there’s no database default behind it.

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