You should read the receipt inkling, through which you can inform the sender that the recipient has received the message, you can reassure the sender. Sometimes, however, when composing a message, you forget to request that you read the receipt by clicking on the menu "tools" → "Request a receipt" in the "Write mail" window, or when you receive a message, annoying the dialog box that frequently pops up and returns a receipt.
In this case, you can select the "request receipts for all sent Messages" checkbox in the "Receipts" tab of the Settings window, so that writing all the messages in Foxmail will automatically help you set up a request read receipt. In addition, for all messages that request a receipt to read, you can automatically send a return receipt, select "Always send a read receipt" on the "return to read receipt" option, and if you do not want to do so, you can choose "Never send a read receipt" to refuse to send a receipt message.