There is an issue with the Kindle Cloud Reader that has been an issue at Amazon for a very long time. The Kindle Cloud Reader was first released in August 2011. I'm posting online so this issue is indexed on Google and others see that this is still a software bug. Amazon has been lazy by putting this into their "not important" software bug list.
Amazon's MOBI eBook format files transferred to Kindle should show up in all Kindle apps, but they don't.
If you download an eBook from Packt Publishing for example, in the
*.MOBI file format, and then email that file to your firstname.lastname@example.org, assuming the FROM email address is in the allowed list, that eBook shows up in the Kindle apps, except the Kindle Cloud Reader. The eBook shows up in the other Kindle apps, except the Kindle Cloud Reader.
Is there a workaround for this issue? When will Amazon fix this?