This is a frequent problem with Outlook 2016.  When opening outlook, you receive the following errors:

Outlook cannot log on. Verify you are connected to the network and are using the proper Server and mailbox name. The Microsoft Exchange information service in your profile is missing required information. Modify your profile to ensure that you are using the correct Microsoft Exchange information service.

System resources are critically low. Close some windows.

Cannot Start Microsoft Outlook, Cannot open the Outlook Window. The set of folders cannot be opened. The information Store could not be opened.

This is happening because the local hidden XML files containing the autodiscover information have been corrupted or otherwise contain bad data, sometimes as a result of an autodiscover DNS record being changed some time in the past.

Browse to:

C:\Users\{Username}\AppData\Local\Microsoft\Outlook\16  (the ’16′ folder is hidden, so change the view setting to see it)

Delete or move any XML file you find that contains the affected email address in its name.

Now Outlook should open OK.

If the problem keeps coming back, marking the corresponding XML file as read-only after it is fixed will stop that.

HINT: Here’s how to get the required XML manually if you have to recreate this file yourself:

Open Outlook with any working account, even a dummy temporary profile.   Then, locate the Outlook icon in the system tray by the clock, hold down CTRL and Right Click, then select “Test E-Mail AutoConfiguration.”

Enter the problem email address and password and click the test button. When it’s finished, if there are office365.com settings within the results, click over to the XML tab and copy everything there into a replacement XML file in your %localappdata%\Microsoft\Outlook\16 folder.

If you have multiple clients behind a NAT router which is connected to another network segment which contains a file server, only one of those clients will be able to use the server’s files at a time because, to the server, all these clients come in on the same IP address.

This happens because SMB is designed to assume any new connection from the same IP address as an existing connection is a duplicate and it tears down the first one.

The easiest fix is to simply block port 445 (direct hosting) at the NAT router so this traffic cannot reach the server from these clients behind the router.  This forces the use of NetBIOS over TCPIP instead of SMB.