O365 Group autoreply to external email address

Hey VinceMHAW ,

What Peter suggested works great and is pretty straight forward to setup, given that you just want to send an automatic reply. However, this works just as an out of office reply, which means that it will only be sent once in 24 hours to one specific sender. If there is an external sender sending multiple emails he will only receive a response for the first email he sends out.  Plus, since you will be using powershell it limits you to stick to simple text. A more robust solution for your use case would be to use Flows( Power Automate) That way you can control from what mailbox the reply is being sent out, how the email will look, extract attachments from incoming email, send alert emails to others and so on. So you can make your automatic response to an external sender look somewhat like this :

The flow structure would look somewhat like this:

Dive deeper: 

https://powerusers.microsoft.com/t5/General-Power-Automate/Flow-to-generate-auto-reply-email-for-after-hours/td-p/250200

Thanks