Every deal is different so this is all speculation. A common theme with a private equity buyout of company like Rackspace is to break it up into pieces that can be sold as a unit.
Mailgun meets that criteria, it has all of the components of being a full 'company' or can get the ones it was missing, and it has a customer base, product, and revenue (and its profitable according to the post).
So someone bought Mailgun and that owner is treating it like a separate company. Sometimes its the original founders that buy it back, sometimes it is another firm that thinks they can do a bit of work and then sell it or take it public.
Other things that are typically sold off are real estate holdings, patents and other IP, trademarks, and sometime infrastructure contracts. So if for example Rackspace had a long term contract to host company X, they might sell that contract to another Colocation company like Equinex or Coresite.
The idea is that you can sell off all the bits for more money than you paid originally and make a profit. It is not unlike buying a wrecked car and selling it off for parts.
Mailgun meets that criteria, it has all of the components of being a full 'company' or can get the ones it was missing, and it has a customer base, product, and revenue (and its profitable according to the post).
So someone bought Mailgun and that owner is treating it like a separate company. Sometimes its the original founders that buy it back, sometimes it is another firm that thinks they can do a bit of work and then sell it or take it public.
Other things that are typically sold off are real estate holdings, patents and other IP, trademarks, and sometime infrastructure contracts. So if for example Rackspace had a long term contract to host company X, they might sell that contract to another Colocation company like Equinex or Coresite.
The idea is that you can sell off all the bits for more money than you paid originally and make a profit. It is not unlike buying a wrecked car and selling it off for parts.