Updated August 30th, 2019.
Activating Microsoft Office 2011 for the Mac using the built-in online activation wizard seems to be broken. Maybe it’s because Microsoft “end of lifed” Office 2011 in September 2017 (read Microsoft’s announcement about it here). You enter your Product Key, you click the “Activate” button… and you get a message about the activation server being unavailable and a recommendation to try again later. You try again later and it still doesn’t work.
So you try the “Activate by Phone” option. Activating by phone sometimes works and sometimes doesn’t. (Update: it worked for me 8-5-2019 on Microsoft Office 2011 Business.) It’s a totally automatic system– read off a bunch of numbers on your screen (you can speak them, so you don’t have to type them into your phone), then type the numbers that the recording gives you, and then click “Activate.” If it works, it’s magic.
If it doesn’t work, try calling Microsoft Sales & Support and telling them you’re trying to activate Office 2011 for the Mac. The Microsoft Sales & Support person will ask you to read off the Activation Code that you see on your screen, then give you a very, very long number, which you can type into the boxes in the Microsoft Office 2011 for the Mac activation wizard, and that should take care of it.
Here’s the phone number that’s worked for me.
Another option: call Microsoft’s general support number (1-800-936-5700) and say “Office for Mac Activation Department” to the robot that answers. That will get you started down the right path.
There’s a chance that things still won’t work. The reason for this could be that you’ve moved Office 2011 for the Mac to a new machine, or to a new hard drive, by cloning the drive. For example, if you decide to replace your hard drive with something better– I like the Solid State Drives (SSDs) from Crucial-– you’ll be asked to activate Office 2011, and in that case, you’ll never be able to… because each installation of Office is “keyed” to the hardware it’s originally installed on, and that includes the hard drive, and the Activation ID and Confirmation ID will only work on that particular configuration. In that case, you have to get rid of the Office registration files that remember what the original hardware was, and then reinstall, and then enter your Product Key, and then– finally!– do the “Activate by Phone” method.
This link from Microsoft tells you how to clear out those older registration files.