A lot of Office 365 or Microsoft 365 users are having trouble viewing or getting access to the public folders within their organization. When they try to click the public folders, they are blocked with the message,
“Cannot expand the folder. Network problems are preventing connection to Microsoft Exchange”.
If you have encountered the same problem, check out the solutions below on how to fix it on Outlook or OWA.
How to Troubleshoot and Fix Unable to Access Public Folders on Office 365

#1 – Double Check the Folder
It is possible that you cannot access the folder because it was deleted. First, make sure that the folder still exists.
- On your computer, click Start.
- Search for PowerShell and click the app to launch.
- Enter the command, Get-Mailbox -PublicFolder -SoftDeletedMailbox
- Now, check if the folder you are trying to access is found in the result. If it is, it was deleted. You can check the deleted items in your Office 365.

#2 – Access Your Folders Using A Different Computer
Some users say that they can fix the problem by using a different computer. You can also create a new profile on the new computer and delete the ones from the previous pc.
#3 – Make Sure the Users are Members of the Public Folder
Unfortunately, nonmembers of a Microsoft Exchange public folder can not have access to it. If the users are not members, you can easily add them using the steps below.

- Access the Exchange Admin Center.
- Click Public Folders.
- Look for the public folder in question.
- Navigate to the Folder Permissions.
- Click Manage.
- Now, check the members.
- Add the users that are not found in the member list.
- If their names appear on the list, you can remove and add them again.
#4 – Match Email Address in the AutoDiscover

One of the reasons for the error is when the AutoDiscover cannot find the email address in the public folder mailbox. To resolve the issue, you may want to change the email address of your public folder mailbox and use the email in the Microsoft Exchange AutoDiscover records.
If you still encounter the same error after trying the methods above, the best solution is to contact Microsoft support and report the error. You can also visit this page that discusses about setting up Exchange Server public folders for a hybrid deployment.
Did any of the above solutions work for you? Tell us in the comments below.