Same issue I am seeing on other threads, but with no answer. Emails stuck in queue with 421 service temporarily unavailable.
1) Emailed investigation@review.symantec.com and their response is "The IP address is not blocked or bring throttled by our reputation services" so sending IP isn't blocked.
2) Check MX record configuration on receipt domain that is utilizing Symantec Email Security. Looks right to me.
5 cluster1.us.messagelabs.com
10 cluster1a.us.messagelabs.com
3) Running NSLOOKUP from my server shows that DNS is resolving properly.
> server 8.8.8.8
Default Server: google-public-dns-a.google.com
Address: 8.8.8.8
> set type=mx
> abr.com
Server: google-public-dns-a.google.com
Address: 8.8.8.8
Non-authoritative answer:
abr.com MX preference = 5, mail exchanger = cluster1.us.messagelabs.com
abr.com MX preference = 10, mail exchanger = cluster1a.us.messagelabs.com
>
4) SMTP logs shows the following lines.
421 Service Temporarily Unavailable,
attempting to connect
,QUIT,
,221 mail555.messagelabs.com closing connection,
Originally though it was a TLS negotiation issue so created a separate send connector without using TLS. This seems to have worked with a few of the domains using Symantec Email Security. Others are still stuck in the queue.
Any assistance appreciated.