The reply-to address can be freely determined on the Template. Also, the recipient can freely change the reply-to address.
If we are setting up an auto-responder and the custom domain is correct, any character string before the ＠ mark - local prefixes will work.

Currently:

Even if local prefix has been changed by the recipient, Acoustic Campaign will send auto response.

Concern:

Anyone who knows the custom domain can change to various strings the local prefix to prank mail.