Is there a way to save documents to my amazon account besides STK for web?

[luigi rovatti]

The problem is this: I regularly bought a book from Amazon. I then removed its DRM, converted it to epub, tried uploading it to send to kindle for web, it was rejected. I tried converting epub to epub, rejected again. I tried converting it to mobi, then to epub, rejected again. Checked for errors on epub.se, nothing found. Now, I'm aware that I can sideload books into my kindle directly, but if I change kindle, I cannot access that document, and if I delete the book from my kindle, it's saved to the account, so I need that feature.

I understand there's some STK feature available on calibre, I already have my kindle email added to calibre, with the email sender also added.

In any case, the question is if I can send documents to kindle wirelessly to my account besides the web version of STK.