If your store has Block IP Addresses to Admin enabled under IP Firewall, Autoresponder Max IP addresses must be added to the Allow list. To do this, navigate under your Volusion Admin to Settings ⇢ IP Firewall ⇢ + Add. Provide these details for the fields (a separate record for each IP address):
IP Range Begin / IP Range End: 18.104.22.168, 22.214.171.124, 126.96.36.199
Allow or Block: Allow
Applies To Admin Area Only: Checked
Please also see the Volusion knowledge base article on the IP Firewall.