I had Norton Internet security before. I think you can disable the option to scan outgoing messages. Like you said it is not needed at all. Try to see at the setups in your norton software.
I did the same as you woody, first I had norton's free trail in my laptop when I bought it then I bought Panda. Does where killing my computer speed. Took all the memory. Then I got recommended to Nod32. I when I switched my computer started to run fast.