Hi Sadie,
That Email Proxy only examines messages for threats (worms, viruses, etc). It does not scan for spam: there are other products which provide that protection (Symantec Mail Security for MS Exchange). As far as I am aware it wouldn't be responsible for sending mails like the ones you have added to this forum thread.
All the same, I recommend that, as a best practice, steps are made to ensure that all clients are runnig the latest releases of SEP or SAV, have up-to-date definitions, and all MS patches are applied.
Hope this helps! You may wish to start a dedicated Connect thread for this issue, if it persists.
Thanks and best regards,
Mick