QNAP NAS無法發信 Failed to send a test message using SMTP Service.

在QNAP NAS設定好電子郵件設定，用來發送警告信給管理者，設定好後測試，卻都失敗，錯誤訊息就是示"Failed to send a test message using SMTP Service."。

從不同網段連到QNAP的管理web都正常，所以就覺得網路設定都沒問題。

後來就想用ssh連上QNAP，去ping在不同網段的mail server，卻是不通的，然後再執行route -n 顯示路由表時，卻沒有0.0.0.0的路由，這就妙了。

本來想直接用指令去加，但查到的指令route add default gw 192.168.24.1 br0有錯誤，所以就決定回管理web上看看是不是少設了什麼。

結果發現了一個東西，有一個系統預設閘道的設定，之前都沒去理它，後來進去這設定，在把gateway設定上去之後，回到ssh裡，route -n 顯示路由表時，就有0.0.0.0的路由，發送信件的功能也就正常了。

The QNAP NAS is unable to send emails.

When setting up the email configuration on the QNAP NAS to send alert messages to the administrator and testing it, all attempts fail with the error message "Failed to send a test message using SMTP Service."

Since accessing the QNAP management web interface from different networks works fine, it is believed that there are no issues with the network settings.

Later on, an attempt was made to connect to the QNAP using SSH and ping the mail server in a different network segment, but the connection was unsuccessful. Upon executing the command "route -n" to display the routing table, it was noticed that there was no route for 0.0.0.0, which was puzzling.

Initially, there was a plan to manually add the route using the command "route add default gw 192.168.24.1 br0," but it was found to be incorrect. Therefore, the decision was made to go back to the management web interface and check if anything was missing.

As a result, it was discovered that there was a default gateway setting that had been overlooked. Previously, it had not been addressed. After accessing this setting and configuring the gateway, upon returning to the SSH session and executing "route -n" to display the routing table, the route for 0.0.0.0 appeared, and the email sending functionality started working correctly.