Messages are accumulating in the delivery queue for some domains and cannot be delivered from Symantec Messaging Gateway (SMG).
Viewing the delivery queue, messages are queued with the status "450 4.7.1: Helo command rejected: Host not found".
Mail servers may perform a DNS check to resolve the hostname provided by the sender in the SMTP EHLO command and defer the connection if the IP for the EHLO hostname either does not exist or does not match the connecting IP.
This is similar to the the SMG DNS validation option "Reject connections where the domain provided at HELO and EHLO has neither an 'A', nor an 'AAAA', nor an 'MX' record in DNS"
Ensure that the MTA hostname has an associated DNS address record and that the SMG public IP matches the DNS address record.
To change the MTA host name:
Once the changes are applied, retry the mail delivery: