I have a user, where I want him to still have his mail access, but I want to remove him from all the groups he is in.
There are about 15 groups.
I know I can go into each of them, and do it manually, but is there an easy way? one button ?
I suggest using a free admin management tool like FlashPanel, available from the Google Apps Marketplace.
Once setup, open the app and go to users then select the user you want to remove from groups.
Select Groups and then click each red X in the Actions column of the list of groups you want to remove them from.
This is not a "one button, all-groups" approach but it is faster than editing each group in Control Panel.
Here is the link to the Google Apps Marketplace FlashPanel app: https://www.google.com/enterprise/marketplace/viewListing?productListingId=14304+18345705634006699039&category=&query=flashpanel