1.5.8. gave us this "nice" option....
is there someone who can write an addon to not see this box anymore?
I think it was added as a security measure after an addon sent people's gold to another player without any notifications. Not sure if it can be disabled.
I haven't looked into trying to break it, but the whole point was to have a confirmation on sending a mail that contains attached gold or items which could not be overwritten.
So to answer the question, no I wouldn't think this dialog can be skipped like the delete confirmation.