As an IT administrator managing Exchange Online, you know the drill: It's 4:30 PM on Friday, and suddenly users can't access a shared mailbox. Or emails aren't being delivered. Or permissions that worked yesterday mysteriously stopped working today.

Here are the 7 most common Exchange Online issues and exactly how to fix them.

Issue #1: "Access Denied" to Shared Mailbox

Symptom: User can't open a shared mailbox they should have access to.

Common causes:

  • Permissions not properly assigned
  • Recent permission change hasn't propagated yet
  • Outlook cache is stale
  • User needs Full Access AND SendAs permissions

Fix:

  1. Verify permissions in Exchange Admin Center
  2. Check both "Full Access" AND "Send As" are granted
  3. Wait 15-30 minutes for permissions to propagate
  4. Have user restart Outlook
  5. If still failing, remove and re-add permissions

Prevention: Use BUTTER to manage permissions in bulk. It shows you exactly which permissions are assigned and makes bulk changes instant instead of clicking through each user individually.

Issue #2: Can't Add Members to Distribution List

Symptom: Error when trying to add users to distribution list, or users don't appear after adding.

Common causes:

  • Not using a mail-enabled security group (wrong group type)
  • Insufficient permissions to modify the list
  • User doesn't exist or is external
  • Cached data in admin center

Fix:

  1. Verify you have Owner permissions on the distribution list
  2. Check the user exists in your tenant
  3. Use PowerShell if the admin center fails: Add-DistributionGroupMember -Identity "ListName" -Member "user@domain.com"
  4. Wait 5-10 minutes and refresh

Better solution: Stop fighting with the admin center. BUTTER accepts lists of users in any format and adds them all at once. Paste 100 names and you're done in 2 minutes instead of 30.

Issue #3: Emails to Distribution List Not Being Delivered

Symptom: Emails sent to a distribution list aren't reaching some or all members.

Common causes:

  • Sender restrictions on the list (only certain people can email it)
  • List is set to only accept internal mail
  • Member mailboxes are full
  • Messages stuck in moderation queue

Fix:

  1. Check distribution list settings ? "Delivery management"
  2. Verify "Only senders inside my organization" if external emails should work
  3. Check if moderation is enabled (messages waiting approval)
  4. Test by sending from different accounts
  5. Check message trace in Security & Compliance Center

Issue #4: "Send As" Permission Not Working

Symptom: User has Send As permission but can't send email as the shared mailbox.

Common causes:

  • Permissions haven't propagated (can take up to 60 minutes)
  • Outlook needs to be restarted
  • Wrong permission type (Send on Behalf vs Send As)
  • Cached credentials in Outlook

Fix:

  1. Verify Send As permission is actually assigned (not Send on Behalf)
  2. Wait 30-60 minutes for propagation
  3. Restart Outlook completely
  4. In Outlook: File ? Account Settings ? Change ? More Settings ? Advanced ? check shared mailbox appears
  5. Remove and re-add the shared mailbox in Outlook if needed

Pro tip: When assigning permissions to multiple users, use bulk tools to avoid repetitive clicking. Managing permissions individually wastes time.

Issue #5: Shared Mailbox Doesn't Appear in Outlook

Symptom: User has permissions but shared mailbox doesn't show in their Outlook folder list.

Common causes:

  • Automapping disabled on the mailbox
  • User needs to manually add it
  • Outlook cache needs refresh

Fix:

  1. Check if automapping is enabled on the shared mailbox
  2. Manual add: Outlook ? File ? Account Settings ? Account Settings ? Email tab ? Change ? More Settings ? Advanced ? "Open these additional mailboxes"
  3. Or restart Outlook and wait 15 minutes for automap

Issue #6: "User Not Found" When Adding to Resources

Symptom: PowerShell or tools can't find a user you know exists.

Common causes:

  • Using wrong email format (John.Smith vs JSmith vs SmithJ)
  • User is external (not in your tenant)
  • Typo in email address
  • Recent user creation hasn't synced

Fix:

  1. Verify user exists: Get-Mailbox -Identity "user@domain.com"
  2. Check your domain's email format standard
  3. Try alternate formats (firstname.lastname, first.last, flast)
  4. Wait 10 minutes if user was just created

Smart solution: BUTTER includes Smart Format Detection - it automatically tries multiple email format patterns and tells you which one worked. No more guessing.

Issue #7: Can't Create Distribution List or Shared Mailbox

Symptom: Error when trying to create new resources.

Common causes:

  • Name already in use
  • Invalid characters in name
  • Insufficient admin permissions
  • License limitations

Fix:

  1. Check if name already exists (search thoroughly)
  2. Remove special characters from name
  3. Verify you have Exchange Administrator role
  4. Check your M365 license includes Exchange Online
  5. Try PowerShell if admin center fails

Level Up Your Exchange Online Skills

Many of these issues come from not fully understanding Exchange Online's quirks and behaviors. Invest in your knowledge:

Recommended training:

Essential Exchange Admin Tools

The right tools make troubleshooting faster:

Browse our complete IT resources page for more recommendations.

Prevention Is Better Than Firefighting

Most Exchange issues are preventable with:

  • Consistent naming conventions
  • Documented permission standards
  • Regular audits
  • Automation to reduce human error
  • Good monitoring

Spend less time troubleshooting and more time on strategic projects. The right tools and knowledge make all the difference.

Still Stuck?

If you're facing an Exchange Online issue not covered here, check:

  • Microsoft 365 Service Health dashboard (might be a Microsoft outage)
  • Message trace in Security & Compliance Center
  • Audit logs for recent changes
  • Microsoft 365 admin community forums

And remember: our support team is here to help if you need assistance with BUTTER or other Icebox Software products.