The mobi format is Amazon’s proprietary format, compatible with Kindle devices and apps. If you have a .mobi eBook file ready, you can of course publish it via StreetLib. However, it'll only be ditributed to the stores distributing this format.
If, on the contrary, you are providing an ePub file (or asking us to take care of the conversion), the mobi file will be generated automatically. We'll generate a mobi file so it is everywhere where the format is distributed. Amazon will take care of the mobi they distribute themselves.