For SEP 11.0 and SEP 12.0, users are encouraged to support the proposed product enhancement for this feature or funtionality to be included in future versions.
Workaround: use Outlook 2007, Outlook 2003 or another mail client.
However the SEP 11.X Outlook plug-in is only supported on 32 bit versions of the operating systems even with the earlier versions of Outlook.
Alternately, do not use this optional mail plug-in. If a mail security program like Symantec Mail Security for MS Exchange (SMSMSE) is installed on the company's Exchange server or elsewhere in the mail flow (a dedicated mail scanning appliance, for instance) then any threats or other unwanted content should be cleaned long before the messages reach the end users. SEP's optional mail scanning components are of most use only in very small offices or unmanaged deployments. If a proper solution is implemented elsewhere in the mail architecture, then the SEP plug-in adds provides very limited return for its resource usage.
The SEP 12.1 Outlook plug-in is supported for Microsoft Outlook 2010 on both 32 and 64 bit versions
see http://www.symantec.com/business/support/index?page=content&id=TECH141640
best regrads.