How to Send Books from Calibre to Kindle in 2026 (via USB or Email)

"Can I still send books from Calibre to Kindle? I have some books that I downloaded form Libgen, converted to EPUB and MOBI but it never arrives to my Kindle. I wonder if it doesn't work anymore."

Calibre has long been a favorite among Kindle users for its powerful features, such as Kindle DRM removal and the Send to Kindle function. But in an era where Amazon's restrictions are tighter than ever, is sending books from Calibre to Kindle still doable? Absolutely. In this guide I'll highlights two methods—wired and wireless—to transfer books to Kindle from Calibre, complete with troubleshooting tips for when things don't go as planned.

Send Books from Calibre to Kindle via USB

The simplest and most reliable method is to grab your USB cable, connect your Kindle to your computer, and use Calibre's "Send to Device" feature. The books you import can be in either MOBI or EPUB format.

Step 1: Install and Set up Calibre 

Download and install the latest version of Calibre for your computer's operating system from the official website. During installation:

Choose your preferred interface language and select a location for your Calibre library, then click Next.

Select your Kindle model. Choose the manufacturer and the specific model from the menu, then click Next.

On the next screen, you can optionally configure wireless email delivery. If you already have a Send to Kindle email address, enter the required details. Otherwise, click Next to skip this step.

The initial setup is now complete. Click Finish to launch Calibre.

Step 2: Add Books to Calibre

In Calibre, click Add books. In the pop-up window, choose the books you want to send to your Kindle. When the import is finished, Calibre pulls in the book's metadata, cover, and other available details.

Step 3: Send Books from Calibre to Kindle via USB

Use a USB cable to connect your Kindle to your computer. Calibre should detect the device automatically. Once connected, an On Device column will appear next to the book list.

Select one or more books, right-click, and choose Send to device > Send to main memory.

If the books are already in MOBI format, the transfer starts right away. If it's an EPUB book, Calibre will ask whether you want to convert them. A dialog box will appear asking if you want to convert the format. Click Yes to proceed. Calibre will first convert the book to MOBI format and then send it to your Kindle. If you want to check the task progress, click on "Jobs" in the bottom right corner of the interface.

Step 4: Eject Your Kindle Device

Once the transfer finishes, click the Device > Eject this device from the drop-down menu. After that, you can unplug your Kindle from the computer.

Send Books from Calibre to Kindle via Email

Another way to send books to Kindle from Calibre is via wireless transfer through email. Essentially, this method authorizes a sender email in Calibre. Calibre then sends the book from that email to your Kindle email address, and the file syncs to your Kindle device. The following part is how to set up Calibre to send books to your Kindle in this way:

Step 1: Configure Calibre's email settings

Open Calibre > Preferences > Sharing > Share via Email.

Click Add email to add your Kindle email in Calibre and set it as default.

Set Formats to EPUB only (remove MOBI from the list if it's there). 

Step 2: Whitelist Your Sender Email in Amazon

Go to amazon.com > Account & Lists > Content & Devices.

Open Preferences > scroll to Personal Document Settings. Under Approved Personal Document E-mail List, click Add a new e-mail address and add your sender email. When the sender email appears in the list, whitelisting is complete.

Step 3: Generate a Gmail APP Password for Calibre

A. Enable POP3/IMAP/SMTP services on Gmail.

Sign in to Gmail > click the gear icon > See all settings.

Go to Forwarding and POP/IMAP:

• POP download: choose Enable POP for all mail or Enable POP for mail that arrives from now on
• IMAP access: choose Enable IMAP

Click Save Changes.

B. Enable Two-Step Verification

Log in to the Google Account Security Center. 

Click Security > Two-Step Verification > follow the prompts to bind your phone number and enable it.

C. Generate an App Password  

In Security, open App password generated.

Enter a name (for example, Calibre-Kindle), and then click Create.

You'll get a 16-character app password (example: "abcd efgh ijkl mnop"). Copy and save it. Remove spaces when using the password.

D. Set up email server fields in Calibre

Enter the sender email details in Calibre's email server fields:

• Hostname: smtp.gmail.com
• Port: 587
• Encryption: TLS
• Username: Enter your sender's email address
• Password: Input the 16-character app password generated earlier

Then click Test email to verify Calibre can send successfully.

Step 4: Send EPUB Books to Kindle from Calibre Wirelessly

Return to the Calibre main interface and click Add books to import the EPUB files you want to send.

Select the books you want to send. Go to Connect / Share > choose Email to …

Connect your Kindle to Wi-Fi and wait for delivery. Once received, you can open and read the books on Kindle.

Troubleshooting: Common Calibre Send to Kindle Problems

Even if your settings look correct, sending books to Kindle from Calibre can fail for reasons that aren't obvious, especially with email delivery. Below are the most common real-world problems readers run into, what they usually mean, and the quickest fixes you can try before switching to a more reliable method like USB transfer.

1. Test email fails with Gmail (SMTP 535 / BadCredentials)

Symptoms: Calibre test email shows SMTPAuthenticationError (535) Username and Password not accepted.

Why it happens: Gmail has become increasingly hostile to third-party SMTP sending, and Calibre's official FAQ notes Google has "broken" SMTP support and recommends using a different provider. 

Fixes:

• Use an App Password (requires 2-Step Verification).
• If you are using a Google Workspace account (company/school), App Password/SMTP may be blocked by admin policy.
• Instead of using Gmail, switch to another sender mailbox (such as GMX or Outlook). For GMX configuration, you can refer to the following guide: https://gist.github.com/aminalhazwani/dc161f32024f63291a9f0157a8ce1627

2. E999 "Send to Kindle Internal Error"

Symptoms: Amazon may send a failure email with a message like "Internal send to kindle error E999" or "E999 - Send to Kindle Internal Error."

Why it happens: E999 is often related to EPUB file structure or metadata issues. In many cases, the file has already been uploaded to Amazon, but it fails during Amazon's server-side parsing/conversion process. That's why E999 is more likely a file-level problem rather than an issue with your account settings or network connection.

Fixes:

• Re-download the EPUB and resend it.
• Check and correct metadata in Calibre.
• Go to Edit metadata and make sure fields like Title / Author / Language are complete and reasonable. Filling in missing metadata can resolve Send to Kindle failures.
• Convert "EPUB to EPUB" in Calibre. Convert the book to EPUB again (output format still EPUB), then send the newly generated file. This often rebuilds the EPUB internals and removes details that Amazon's converter may reject, without changing the book's actual content.

3. Kindle never receives the book

Symptoms: Calibre sends successfully, but nothing arrives on Kindle (or arrives only sometimes).

Why it happens: Amazon requires your sender email to be added to the Approved Personal Document E-mail List. Amazon forum guidance explicitly points to this list. 

Fixes:

• Re-check Amazon: Manage Your Content and Devices > Preferences > Personal Document Settings > Approved Personal Document E-mail List. 
• Confirm you're sending from the exact whitelisted address (aliases can break delivery).

Conclusion

Calibre makes it easy to send books to your Kindle. If you want the most stable option, USB transfer is usually the quickest and most reliable. If you prefer wireless delivery, Calibre's email feature can work as well, as long as your sender address is approved by Amazon and you stick to supported formats like EPUB. Keep your library organized, move books to your Kindle smoothly, and spend more time reading instead of troubleshooting.