When SSLv3 option is disabled by Protocols -> Settings -> SSL Restrictions -> Disable support for SSLv3 and earlier protocols in all SMTP TLS conversations, Symantec Messaging Gateway (SMG) 10.6.0-3 and SMG 10.6.0-5 fails to negotiate cipher suites in TLS sessions with MTAs that only support SSLv3/TLSv1.0 protocol.
Symantec has addressed this issue in version 10.6.0-7.
To workaround the issue with version 10.6.0-3 and 10.6.0-5, these temporary workaround options should be considered:
If the receiving MTAs are local, enabling TLS1.2 on the local servers should also be considered.
For Microsoft Exchange servers, see the following information:
Microsoft Exchange 2013:
Microsoft Exchange 2010: