Exchange server throws up some strange errors from time to time. Unfortunately, it is not easy to fix these errors because a lot of them do not give you any information on what is wrong!
One such error that gives no idea of the problem is "Microsoft Exchange is unavailable, Outlook must be online or connected to complete this action." If you see, this is a generic message that can be caused due to a wide range of major and minor problems.
Let's explore the possible causes and the fix for each.
Outlook in compatibility mode
Sometimes, you'll run Outlook in "compatibility mode", either by mistake or without your knowldge. The idea behind this mode is to help Outlook run in older versions of Windows too, but it can cause problems, especially if you have a new version.
The good news is you can turn off this mode easily. To do that,
- Navigate to Outlook.exe file. You can find this file in C:\Program Files [x86]\Microsoft Office\Office 14\ or C:\Program Files [x86]\Microsoft Office\Office 15\, depending on the version you have.
- Once you identify this file, right-click on it and choose "Properties."
- In the dialog box, navigate to "Compatibility" tab.
- Uncheck all the boxes in this tab, if any box is checked. Click Apply > OK.
Finally, restart Outlook and see if your problem is fixed.
Please note this option is not available in Outlook 2016 because 2016 version does not have compatibility mode.
Unable to find mail server through Active Directory
Another possible cause is when your computer is unable to see your domain controller as the global catalog server. So, it is not able to find mail server through the Active Directory.
This is a rather tricky error because we tend to assume by default that the Outlook will find our mail server. And in most cases, it will too.
Nevertheless, it is good to know that sometimes Outlook cannot find the mail server by default.
The fix for this is rather long and complex, as you'll have to make changes to your registry. So, close Outlook and open your registry by entering "regedit" in Windows + Run.
First off, you need to make some changes to the registry, so a good practice is to take a backup of the existing registry settings before you make changes to it. One way to take a backup is select "computer" located at the top of your registry tree. Then, click File > Export.
Next, look for a value called HKEY_CURRENT_USERSoftwareMicrosoftExchangeExchange Provider. Create a string value to this registry key. Give the value name as "DS Server" and the value data should be FQDN of your global catalog services domain.
Now if you open Outlook, this error should be fixed, provided the problem was in finding the mail server through Active Directory.
RPC encryption
Another possible cause for "Microsoft Exchange is unavailable, Outlook must be online or connected to complete this action" error is due to RPC encryption in your Outlook profile.
There are two ways to fix this error. The first one is to manually update an existing profile while the second option is to disable the encryption requirement on all CAS servers.
To implement the first option,
- Go to Control Panel, and open Mail
- Select Show Profiles
- Choose your profile from the list and click properties
- Next, select "Email accounts"
- Select "Microsoft Exchange [send from this account by default] account > change"
- A dialog box will open and in that box, click "More settings"
- In the next dialog box, navigate to "security" tab.
- Finally check the "Encrypt data between Microsoft Office Outlook and Microsoft Exchange" box. Click OK.
This should fix the problem for you.
The second option, which is to disable encryption on all CAS servers, is a solution that is NOT recommended by Microsoft due to security reasons. But, if you would still like to use it, run the following command on Exchange Management Shell.
Set-RpcClientAccess –Server –EncryptionRequired:$False
This will disable encryption.
To enable it again, run this command.
Set-RpcClientAccess –Server –EncryptionRequired:$True
Corrupted OST file
The most common cause of this error is a corrupt OST file. This file can get corrupted due to a variety of reasons, such as:
- Faulty hardware components or bugs
- Interruption due to network connectors
- Bad sectors on the hard drive
- Sudden surge or loss of power
- Large file size
- Dirty shutdown
- Incompatible Outlook Add-in, and more.
One way to fix this error is to rebuild your OST file. But this could cause the loss of your existing data.
A better option is to use third-party tools like Stellar OST to PST Converter.
Conclusion
Stellar OST to PST converter is a tool that extracts contents from a corrupted OST file and saves them in a new PST file. You can open this new file in Outlook and access all your data again. This tool ensures that there is no data loss during the conversion.