Sending an encrypted message is like sending your correspondence in an envelope rather than a postcard; it makes it difficult for other people to read your message.

发送加密消息类似于使用信封而不是使用明信片给收信人发送信件；这使其他人很难读到您的信息。

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Sending an unencrypted message is like sending your correspondence in a postcard instead of an envelope.

发送未加密的消息类似于使用明信片而不是信封给收信人发送信件。

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And even for those who admitted to buying the occasional postcard, the effort of actually sending them was sometimes a bridge too far.

CNN: Can postcards survive in the digital age?