Why is Autoresponder sending messages saying "Mail failure - no recipient addresses"?
The message occurs when the auto-response email cannot be delivered. The 'bounce' email comes back to the server. The server attempted to send the user's 'bounce' email, returning to Autoresponder. Autoresponder then ignores the 'bounce' email.
You can see if Autoresponder rejects the 'bounce' email message by looking in the
.autorespnder/info_log file inside the cPanel user's home folder. The entries for the rejected messages look similar to the following.
[2021-09-01 11:27:18 +0200] info [autorespond] From matches commonly used mailer daemon address, skipping auto reply
You would need to determine why the emails bounced to stop receiving the message. We have a few support articles that can help start the search.