In Outlook 2003 when I received a meeting invite I could click the Accept button once to accept it. In Outlook 2010 I have to click Accept, then click "Send the response now", which is completely useless - what else do I need to say other than "yes, I'll be there"? How do I restore the old behaviour so that a I can accept with a single click? (Declining is different, of course - I might want to edit the message then.)
There is an answer. It is a bit long, so hold on.
The following process has to be executed only once.
When you receive an invite, DO NOTHING in the way of responding. Instead, in the message window click File. This opens the File window. On the left side, click Options. The Outlook Options window opens.
(Note: You HAVE to do this from the message, not from any other Outlook screen, because this is context-sensitive.)
Now, click Customize Ribbon. Click once on the "Message" entry in the right-hand pane (so as to select the main tab), and then click the New Group button located on the bottom-right. This creates a new group. Optionally, right-click to rename it as "Die MS Die".
Click once to select the new group. Then, in the top-left pane, select "All Commands" (the default option is "Popular Commands"). Scroll down to find a command named "Send the Response Now". It will not surprise you that there are three of those with no clue whatoever. Choose the LAST ONE, and click the Add button (between the left and right panes) so that this option gets added to the new group. Optionally, right-click on it now to rename as "Single Click Accept" and also change the icon. Click OK.
When you return to the message, the new group will be displayed in the ribbon and it will contain only one button, named "Single Click Accept" or the older name.
NOTE: If this ends up rejecting instead of accepting, please try another of the three "Send the Response Now" buttons. Believe me, one of these is the one you want.
I can't help you with a mouse click based solution but you can have a look at my question for a shortcut key based solution.