When attempting to deliver messages outbound to the internet, some messages becomes stuck in the delivery queue with a "no MX or A for domain" message even though a lookup of the domain's MX records returns valid mx hosts. Looking up the DNS records shows something similar to the following:
domain.org. 1951 IN DNAME domain.com.
mx.domain.org. 1951 IN CNAME mx.domain.com.
mx.domain.com. 1951 IN MX 10 smg3.domain.com.
mx.domain.com. 1951 IN MX 10 smg1.domain.com.
mx.domain.com. 1951 IN MX 10 smg2.domain.com.
454 4.4.4 [internal] no MX or A for domain
2014 Jul 29 09:42:24 PDT (debug) ecelerity:  LT-00284 inserted 80/00-08666-0FEC7D35 into lookuptable (calling dns_get_MXs)
2014 Jul 29 09:42:24 PDT (debug) ecelerity:  ARES_00320 process dns response 17465 [mx.domain.org]
2014 Jul 29 09:42:24 PDT (info) ecelerity:  smsrouting: DNS reply to MX lookup of \'mx.domain.org\': wrong answer name \'domain.org\'; unroutable messages may be stuck in domain container \'#sms#00000005\'
Some DNS servers return the DNAME record as part of the response to the MX record lookup. The SMG mail server does not understand the DNAME record and so does not process the DNS response.
Some DNS servers do not respond with the DNAME record as part of the MX record response. SMG systems which use Microsoft Exchange as their primary DNS server do not appear to be affected by this issue as MS Exchange leaves the DNAME record out of the DNS response. Use of the DNAME record type in DNS is very limited so this issue is unlikely to much effect on outbound mail delivery.
This issue has been addressed with the Messaging Gateway 10.6.2 release.
Please see the Messaging Gateway Administration Guide for detailed instructions on how to update the SMG software.