I have been discussing this with 1 of my contacts in McAfee and from what i gather what I said seems to be correct. ie scan attachments only on opening and outgoing scan attachments seem to be covered by Anti spam.
I asked for clarification
Perhaps it doesn't make much difference, but I would be more comfortable knowing that TP is identifying and protecting against threats when they arrive in my inbox rather than waiting until I actually open them. But maybe that's just me.
Thank you for the input, everyone.