The locations where wrong for me. I found them at, C:\Program Files (x86)\Opera\profile\mail
That's a non-multi-user install that's not really recommended for installation in the program files folder. In this case, the local and roaming profile folder files and folders are all mixed together in the "profile" folder. So, you just have to copy the files and folders to the proper spot in the local and roaming profile folders for Opera Mail.