zuì ān quán de xí guàn shì xiě wán zhèng wén yǐ hòu, zài jiǎn chá yī biàn shōu jiàn rén, chāo sòng rén hé fù jiàn

最安全的习惯是：写完正文以后，再检查一遍收件人、抄送人和附件。

The safest habit is to check the recipient, CC, and attachments again after finishing the body of the email.