And with gmail you have to go into gmail settings and allow third party apps as well. Much easier to use gmx. All this has been documented in exhaustive detail in the calibre FAQ for years. Just follow the instructions in the FAQ and you will be fine. All that's changed recently is that amazon has started blocking more mails that are sent without using a well known mail relay than it used to before. Therefore, it is critical you setup a mail relay, preferably, GMX as described in the FAQ.
http://manual.calibre-ebook.com/faq....-using-calibre