E-mail viruses are detected & stopped by the corresponding resident providers: Outlook plugin for full Outlook and Exchange, and Internet Mail for any other POP/IMAP/SMTP e-mail clients. So, they are detected before they arrive to your mailbox. In case of full Outlook, I think the scanning can be performed even on viewing.
But I guess that's not what you were asking about. Well, I think that if you use an unpatched (buggy) Outlook and preview the infected message, it will be catched by the "executable" scanner as well - since the virus will be executed, and that's what the Standard Shield is looking for.
As for the updates (I guess you mean the virus database, not the software itself) - if no dangerous virus appears, the database is updated twice a week (but if a dangerous virus starts spreading, such as Sobig recently, the update is released immediatelly, even multiple updates during one day). So, it's easily possible that there was no update since August 22, and when you performed the manual update, you got the one just released. You can check your configuration of the updates in the program Settings.