IPv6 MX preference causes outbound delivery failures.

Products

• Messaging Gateway

Issue/Introduction

Outbound mail delivery fails with "421 4.4.0 [internal] Failed to connect: no mail servers for this domain could be reached at this time" for external recipient domains, for which MX records include IPv6 (AAAA) with dual stack MX record wherein IPv6 and IPv4 both are enabled.

Resolution

Capture problematic domain name and set non local route using SMG to point out to IPv4. 

Log in to SMG and go to Protocols/Domains/Add/Delivery and insert domain name pointing to IPv4 destination host.