+ 0 Votes firewall jknowles 7 years ago I had the same issue. Turns out somehow all of my client computers had Windows firewall turned on after an update. Simply turning the Microsoft firewall off, on each client, in control panel did the trick. + 0 Votes Problem solved! alanb 7 years ago Rather than turn the firewall off we discovered that adding the Outlook program to the exception list produced a more secure result - this we are applying through a GPO to ensure consistence across the domain. Thanks for the help.