In most cases this has a very simple fix,
For some reason your WebClient service is not starting, you can go in and manually start it in order to initiate the WebDAV mapped network drive. To do this, open services, scroll down to "WebClient" and start it.

Then proceed to setup your network drive as normal.
You can do this with a registry change,
Whenever making registry changes be sure to do a full backup first, I am not responsible for your mistakes.
Open your registry editor (regedit)
goto
Computer\HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced
right click on advanced and add new DWORD value "JumpListItems_Maximum" and assign the desired value in decimal format.

In most cases you do not need to restart anything, if you would like you can restart explorer using the task manager.
open task manager: Ctrl+Alt+DEL select task manager and under the processes tab right click on "Windows Explorer" and choose restart.

That's it, your done.
This error generally happens when rdpclip has become unstable. To solve this issue you can simply restart the rdpclip.exe application.
To do this open task manager, click on "Details" then find rdpclip.exe

Now end task on rdpclip.exe
Next you can restart the rdpclip.exe by running a new task

Enter rdpclip and click "OK"

That's it, your done and the problem should be solved.
If you have not already, you can download PuTTY from putty.org
Once you open PuTTY you can input the mail server name or IP address you are attempting to connect to into the Host Name field. Then update the port to 25 and the connection type to "Telnet".

When you click connect you should see something like this:

Other responses:
- If you do not receive a response, the connection was blocked by the mail server.
- If you receive "Cannot connect to host on port 25" the mail server is likely offline or is having network routing issues.
You can also run a few commands to test
You can quickly bypass this error by using robocopy,
use run as administrator to open a command prompt and do the following:
robocopy /e /is /v /eta [driveletter]:\sourcefolder [driveletter]:\destinationfolder
/e Copies all subdirectories.
/is Includes the same files.
/v Produces verbose output, and shows all skipped files.
/eta Shows the ETA of the copied files.