Exchange Online PowerShell

The ExchangeOnlineManagement module connects to Exchange Online. Connect-ExchangeOnline authenticates and imports the cmdlets; Disconnect-ExchangeOnline ends the session.

Lesson 2 min read Windows PowerShell 5.1 and PowerShell 7

Documentation: Microsoft Learn

Written and tested by Dhrub Bharali · Updated 02 October 2026

Overview

The first surprise is that Get-Mailbox returns 1,000 results by default. Not an error, not a warning, just the first thousand. -ResultSize Unlimited is required for any real inventory, and forgetting it produces a report that is quietly wrong in a tenant of any size.

The second is filtering. These cmdlets have -Filter, which runs server-side, and it is much faster than Where-Object for large tenants. The syntax is Exchange's own, so it is another dialect to keep straight alongside AD filters and OData.

The third is throttling. Exchange Online limits how fast you can call it, and a tight loop over thousands of mailboxes will be slowed or blocked. Get-Mailbox once and work from the results rather than calling per user inside a loop.

Remember that mailbox size lives in Get-MailboxStatistics, not Get-Mailbox, so a size report needs both, joined on identity. And TotalItemSize is a formatted string rather than a number, so sorting on it directly sorts alphabetically.

For automation, use certificate-based app-only authentication. Basic authentication is gone.

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Read the command and its supplied arguments. This example requires real PowerShell or its module; this diagram does not execute it.

[pscustomobject]@{
  Connect = 'Connect-ExchangeOnline -UserPrincipalName admin@corp.com'
  Query = 'Get-Mailbox -ResultSize Unlimited | Select-Object DisplayName, RecipientTypeDetails'
  Stats = 'Get-MailboxStatistics -Identity <upn> | Select-Object TotalItemSize, ItemCount'
  Close = 'Disconnect-ExchangeOnline -Confirm:$false'
} | Format-List

Stage 1[pscustomobject]@{Positional values or no named parameters
Stage 2Format-ListPositional values or no named parameters

What happens

This prints the connect, query, stats and disconnect sequence. -ResultSize Unlimited appears in the query line because leaving it out is the single most common error here. The Stats line is separate because size information is not on the mailbox object.

Worth remembering

Get-Mailbox returns 1,000 by default. Use -ResultSize Unlimited.
-Filter runs server-side and uses Exchange filter syntax.
Throttling is real; avoid per-user calls in a loop.
Mailbox size comes from Get-MailboxStatistics, and TotalItemSize is a string.

Primary documentation

Select-Object reference

Try it

Illustrative output · values vary by environment

1PS> [pscustomobject]@{

2PS> Connect = 'Connect-ExchangeOnline -UserPrincipalName admin@corp.com'

3PS> Query = 'Get-Mailbox -ResultSize Unlimited | Select-Object DisplayName, RecipientTypeDetails'

4PS> Stats = 'Get-MailboxStatistics -Identity <upn> | Select-Object TotalItemSize, ItemCount'

5PS> Close = 'Disconnect-ExchangeOnline -Confirm:$false'

6PS> } | Format-List

Example reader

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[pscustomobject]@{
  Connect = 'Connect-ExchangeOnline -UserPrincipalName admin@corp.com'
  Query = 'Get-Mailbox -ResultSize Unlimited | Select-Object DisplayName, RecipientTypeDetails'
  Stats = 'Get-MailboxStatistics -Identity <upn> | Select-Object TotalItemSize, ItemCount'
  Close = 'Disconnect-ExchangeOnline -Confirm:$false'
} | Format-List

Ready to inspect.

Prints the Exchange Online session sequence with the result-size caveat.

Show reference output

Illustrative output · values vary by environment

Connect : Connect-ExchangeOnline -UserPrincipalName admin@corp.com
Query   : Get-Mailbox -ResultSize Unlimited | Select-Object DisplayName, RecipientTypeDetails
Stats   : Get-MailboxStatistics -Identity <upn> | Select-Object TotalItemSize, ItemCount
Close   : Disconnect-ExchangeOnline -Confirm:$false

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