✔ 最佳答案
Check if you have Out of Office Assistance on your Outlook but this function is enable if you are using Microsoft Exchange server as mail server only, if your Outlook is connecting to a SMTP mail server, this function is disable.
Alternative, check if you have a Rule setup function enable, if it is; you can setup a rule to send autoreply message to sender but you need to turn on your computer all the time and the Outlook must be sign on all the time in order to make it work.