RBL delisting - definitely a false positive to be corrected
AT&T/Prodigy is blocking our messages (from a large bank)
Unknown address error 553-'5.3.0 alpd683 DNSBL:RBL 521< 184.108.40.206 >_is_blocked.For assistance forward this error to firstname.lastname@example.org
The IP is not new, it has a very well established reputation, messages are 100% signed and authorized, fully DMARC compliant, no marketing.
The email address listed in the error is unresponsive for weeks now.
Looking for human to discuss.