Users of one of my customer have reported that 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.

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.

To do this, please go to File Options Customize Ribbon. Expand Send/Receive tab Preferences. Select Work Offline from the left part and then add it to this group. If the steps above won’t help, we can try repairing Office to check the results. How to Get Out of Offline Mode in Outlook 2016 (Guide with Pictures) Step 1: Open Outlook 2016. Step 2: Select the Send/Receive tab at the top of the window. Step 3: Click the Work Offline button in the ribbon at the top of the menu.

Outlook 2016 Work Offline Greyed Out

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 /safe command) 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.

Outlook 2016 Work Offline Issue

Outlook 2016 Work Offline Keeps Turning On

After that you can run your Lync (Skype4B). The next time Outlook starts online.

Outlook 2016 Work Offline Option

Outlook 2016 Work Offline Hotkey