Kindle Paperwhiteさんの容量は約2GBなので，適宜端末から削除しながら使っていたのですが，容量不足を起こしてしまったようで．
容量不足になるとAmazonから即時メールが来たのですが，その時の文面がこれ．

Your Amazon.com Kindle is out of memory space
We are writing about your Kindle (雪だるまの Kindle). Content is waiting to be downloaded to your device but your Kindle does not have enough memory space left to receive this content. To free up memory, go to the Home screen on your Kindle to remove items you no longer need on your device. Note that a copy of Kindle content you purchase from Amazon is kept at the Manage Your Kindle page on Amazon.com. This Amazon service securely stores all of your Kindle books and recent issues of newspapers and magazines and allows you to retrieve them if you have previously deleted them from your Kindle. You can also retrieve this deleted content from "Archived Items", found on your Kindle's Home screen.

Once you free up space, the waiting items will be automatically delivered to your Kindle. You can also select "Sync & Check for New Items" on the Home screen menu to get new content.

To remove an item from your Kindle, follow these steps:
1. Press the Home button to bring up the Home screen.
2. Use the 5-way controller to choose items from the list.
3. Shift the 5-way controller to the left to remove an item.
4. Press the 5-way controller to complete removal of the item.

You can also connect your Kindle to a computer via the USB cable to move unused files out of Kindle's memory to your computer's hard drive, or delete them using your file browser.

You can see how much space is now available on your Kindle memory by depressing the Menu button. At the top left corner of the Menu screen, you will see the total amount of free memory shown in megabytes.

…Amazon.co.jpのアカウントにAmazon.comのカスタマーセンターから送られてきました．”書き込もうとしてるんだけど容量足りないからなんか削除して！”と言われているのはなんとなく分かるんですけど，分かるんですけど．
Kindle用のサーバー，実はAmazon.comもAmazon.co.jpも同じの使ってるの…？と思ったのでした．