Obviously because of the white labeling it is harder to know who is behind the software.
A couple of examples:
[1] Dell - https://partnerdirect.dell.com/sites/channel/en-us/documents...
[2] Rackspace - https://www.rackspace.com/en-us/email-resellers
[3] IBM https://www-03.ibm.com/press/us/en/pressrelease/35592.wss
If you are interested in finding more companies that white label, check out CRN.com - http://www.crn.com/search-results?searchterm=%22white+label%...
They would've gone out of business years ago if it weren't for their white label program. It took a few years for their main site to make more money than the white-label versions.