One of my staff reported that their Outlook always starts in the offline mode. Obviously, e-mails cannot be sent or received, and the Outlook icon in the system tray has a red cross on it with the following message: “Microsoft Outlook is offline”.
To disable Outlook offline mode, each time a user has to press the corresponding button (“
Work Offline“) on the Send/Receive tab. But the next time you start Outlook, it starts offline again. You have to disable offline mode again in the Outlook settings. It is clear that the constant need to switch Outlook from Offline to Online is terribly annoying to users.
If there is no “Work Offline” button, it means that the Cache Exchange Mode is disabled in your Outlook.
Only some users with Outlook 2016 or 2013 face this problem. User mailboxes are located on an Exchange server and there are no connectivity problems and no errors in the Exchange logs.
Outlook can automatically go offline in case of any network/Exchange connection problems (after 10 failed attempts to connect to the mailbox server). So first of all, we checked the network operation (switches, routers, firewall rules) – everything worked normally.
Here is what else we checked when diagnosing the problem:
- The accessibility of a mailbox through the OWA interface: the mailbox was available;
- In Exchange 2010, you need to check the CAS server availability from the user computer thought port TCP/135 (RPC locator). You can do it using the Test-NetConnection cmdlet:
tnc ber-msgcas –port 135– the port is available. In Exchange 2013/2016, the main protocol for connecting Outlook clients to CAS is HTTPS (MAPI over HTTP), so it suffices to check the availability of port TCP/443;
- We started Outlook in the Safe Mode (
outlook.exe /safecommand) and disabled all Outlook add-ons: the problem persisted;
- We tried to delete an Outlook profile and re-create it again. We reinstalled and repaired Outlook – nothing helped.
The solution was unexpected: all users who reported Outlook start offline problem had Skype for Business (Lync) installed. As it turned out, if Lync and Outlook are started at the same time, changing Offline mode is not saved after Outlook is closed (Lync somehow blocks saving offline mode settings, maybe, due to its constant connection to Exchange).
Thus, to disable running Outlook in the offline mode, you just have to
close Lync / Skype4B (make sure that there are no processes in the Task Manager) and
disable Work Offline mode in Outlook.
After that you can run your Lync (Skype4B). The next time Outlook starts online.