This is interesting, as most links I've found addressing this question of multiple sends of attachments (the problem I'm having) say something to the effect of
"The most common reason for many copies of the same email being sent can be traced back to your mailware or virius scanning tools attempting to scan outgoing messages."
So even if Emsisoft doesn't do this, I'm surprised you've not heard of such a thing.
Can you confirm that my problem with Outlook (sending an email with attachments repeatedly at roughly 3 minute intervals) is nothing to do with Emsisoft? I've had the same issue with different recipients, and it's always when the email has an attachment, seemingly when it's quite a large one.