Exchange Online and Outlook Troubleshooting Interview Questions &
Answers—USER Mailbox
What is the difference between a user mailbox, a shared mailbox, and a
resource mailbox?
A user mailbox is assigned to an individual user in your
Exchange organization. A shared mailbox allows multiple users to read and send
email from a common mailbox. A resource mailbox is used for scheduling
resources like conference rooms (room mailbox) or equipment (equipment
mailbox).
How would you create a new user mailbox in Microsoft 365?
You can create a user in Microsoft 365 admin center and
assign an Exchange Online license. Alternatively, use PowerShell with
New-MgUser and license assignment.
A user reports they cannot send or receive emails. What are the first three
things you would check?
1. Check mailbox size limits.
2. Verify mail flow and rules.
3. Check connectivity and service health dashboard.
What is the purpose of an archive mailbox, and how would you enable it for
a user?
An archive mailbox provides additional storage for emails.
It can be enabled via Microsoft 365 admin center or PowerShell: Enable-Mailbox
-Identity user@domain.com -Archive
What are some common reasons why a user's mailbox might be disabled or
disconnected?
Mailbox disabled due to license removal, account
deactivation, or accidental deletion.
A user is leaving the company. What steps would you take to ensure their
mailbox data is preserved for legal purposes?
Put the mailbox on Litigation Hold or convert it to an
inactive mailbox after license removal.
Explain the concept of an inactive mailbox and how it relates to
eDiscovery.
Inactive mailboxes are retained after a user account is
deleted and can be searched using eDiscovery for compliance purposes.
How can you secure a user's mailbox from being accessed by unauthorized
users? Name at least three methods.
1. Enable MFA
2. Use mailbox audit logs
3. Restrict mailbox permissions
4. Monitor sign-in activity.
What is the purpose of audit logging for a user mailbox, and what types of
actions can it track?
Audit logging helps track mailbox access, send-as actions,
folder deletions, and non-owner access.
How would you set up a mail flow rule to block all emails containing a
specific word or phrase from entering your organization?
Use Exchange Admin Center > Mail Flow > Rules to
create a rule that blocks emails containing specific keywords in subject or
body.
How would you use PowerShell to find all mailboxes that have exceeded their
storage quota?
Get-Mailbox -ResultSize Unlimited | Get-MailboxStatistics |
Where-Object {$_.StorageLimitStatus -eq 'IssueWarning'}
Write a PowerShell command to grant 'Full Access' permission to a user for
another user's mailbox.
Add-MailboxPermission -Identity targetuser@domain.com -User
delegateuser@domain.com -AccessRights FullAccess
How would you use PowerShell to get a list of all user mailboxes and their
current size?
Get-Mailbox -ResultSize Unlimited | Get-MailboxStatistics |
Select DisplayName, TotalItemSize
Explain the difference between Remove-Mailbox and Remove-Mailbox
-PermanentlyDelete in PowerShell. What are the prerequisites for the latter
command?
Remove-Mailbox soft deletes the mailbox; PermanentlyDelete
skips the soft-delete state. Requires disabled litigation hold and mailbox to
not be on hold.
What is a Litigation Hold, and how would you enable it on a user's mailbox
using PowerShell?
Litigation Hold preserves mailbox content for eDiscovery.
Use: Set-Mailbox -Identity user@domain.com -LitigationHoldEnabled $true
A user's mailbox is full, and they need to make space immediately. What
steps would you recommend they take? What administrative action could you take
to help?
User can empty Deleted Items and Sent Items. Admin can
enable Archive or increase quota for E3/E5 plans.
A user reports that emails from a specific sender are not being delivered.
The sender is not getting any bounce-back message. How would you investigate
this issue?
Check message trace, inbox rules, junk folder, and transport
rules.
How would you troubleshoot an issue where Outlook keeps prompting a user
for their password, but it works fine on Outlook on the web (OWA)?
Reset credentials, check for corrupted profile, verify
Autodiscover, and test with SaRA tool.
Explain the process you would follow to recover a user's mailbox that was
accidentally deleted 5 days ago. What if it was deleted 45 days ago?
Within 30 days: Restore from soft-delete using PowerShell.
After 30 days: Restore via inactive mailbox if litigation hold is enabled.
A user's mobile device is not syncing their email correctly. What are the
common causes and your troubleshooting approach?
Check connectivity, reconfigure profile, check device
compliance, remove/re-add account, and verify ActiveSync settings.
Outlook is 'frozen.' What is the first question you would ask them to
clarify the situation?
Is Outlook unresponsive, crashing, or slow to respond?
What is the significance of starting Outlook in Safe Mode when
troubleshooting performance problems?
Safe Mode disables add-ins and customizations, helping
isolate the issue.
How would you explain Cached Exchange Mode vs. Online Mode to a
non-technical user?
Cached Mode stores a local copy for offline use. Online Mode
always connects directly to the server.
Outlook freezes only when searching – what could cause this and how to fix?
Likely Windows Search indexing issue. Rebuild index or
repair OST file.
What is SaRA, and when would you use it?
Microsoft Support and Recovery Assistant helps diagnose and
fix common Outlook issues like freezing or profile problems.
Proactive steps to prevent Outlook issues?
Apply Office updates, control mailbox size, disable unused
add-ins, implement group policies.
How does Online Archive help with performance, and common user complaint?
Moves older items to archive, improving performance. Users
may complain about difficulty finding archived emails.
Multiple users report freezing – first action and suspicion?
Check service health and network connectivity. Likely
backend/server or update issue.
How can a misconfigured Public Folder cause performance issues?
Large or improperly set Public Folders slow down Outlook for
users with access.
Role of add-ins in Outlook performance and how to disable them?
Problematic add-ins slow Outlook. Disable via File >
Options > Add-ins > Manage COM Add-ins.
Purpose of .OST file, signs of corruption, and repair method?
OST allows offline access. Corruption signs include sync
issues or freezing. Repair via SCANPST or recreate profile.
Mailbox is 50GB and freezing – what should be done?
Enable archive, reduce mailbox size, recreate OST, disable
unused add-ins, upgrade Outlook version.
How to test for slow network issues causing Outlook to freeze?
Use `ping`, `tracert`, Outlook Connection Status
(Ctrl+Right-click Outlook icon > Connection Status).
Windows Search indexing issue causing freeze – fix?
Rebuild search index, repair Office, or switch to Online
Mode temporarily.
A user reports they cannot see old emails in Outlook.
What are your first steps?
- Verify
the user is in Cached Exchange Mode.
- Check
the "Mail to keep offline" slider in Outlook account settings.
- Ask if
they can see the emails in Outlook Web Access (OWA).
- Check
if Online Archive is enabled.
- Ensure
no filters or custom views are applied.
2. What is Cached Exchange Mode and how can it affect
visibility of old emails?
- Cached
Exchange Mode stores a local copy of mailbox data.
- If set
to keep only recent mail (e.g., 1 month), older emails won't appear in
Outlook, but are still available in OWA.
3. How would you resolve issues where a user’s .OST file
might be corrupted?
- Close
Outlook.
- Go to %localappdata%\Microsoft\Outlook.
- Rename
or delete the .ost file.
- Restart
Outlook to recreate the file automatically.
4. What is an Online Archive mailbox and how does it help
with storage?
- An
Online Archive is a secondary Exchange mailbox.
- It
stores older emails based on retention policies.
- Helps
keep the primary mailbox size smaller and improves performance.
5. How can retention policies affect visibility of older
emails?
- Policies
may move older emails to the archive mailbox.
- In
some cases, they may delete emails based on policy duration.
- These
actions make emails no longer visible in the primary mailbox.
6. If emails are missing only in Outlook but visible in
OWA, what does that suggest?
- This
usually indicates a local issue:
- Cached
mode config
- .OST
file corruption
- Incorrect
filters or views
- Indexing
issues
7. How would you troubleshoot Outlook search not
returning old emails?
- Rebuild
the search index.
- Ensure
the Windows Search service is running.
- Start
Outlook in Safe Mode.
- Repair
the Office installation.
- Use
the Microsoft Support and Recovery Assistant (SaRA) tool.
8. What is the role of the .OST file and what are signs
it's corrupted?
- The .ost
file stores offline cached mailbox data.
- Signs
of corruption:
- Emails
missing
- Sync
errors
- Frequent
crashes
- Recreating
the .ost often resolves these issues.
9. Can enabling Online Archive affect user perception of
missing emails?
- Yes,
emails may appear "missing" to users unaware that they were
moved to the archive mailbox due to policies.