Like already stated there is no secure email. If persay you were looking to do this stuff an have minimal chance to get caught this is what you do. (This guy at the gym told me about his routine when he was trying to get me to order stuff, but I won't take steroids illegally, I will do HRT next year though)
1. Get a cheap laptop from someone in the paper or whatever. They won't know ur name or anything.
2. Make sure it has a wireless card, then be sure to drive around until you can find a connection.
3. Place your order and only use that computer and different connections in different locations when you want to check those emails lol.
4. Do not leave the computer at your house obviously, if you can leave it with a trusted person that you don't call with your landline or cell phone. This makes it almost impossible to tie orders to you because they can't find the computer you did stuff with. Even if they use the dealer's how are they going to prove it actually is you if its not your ip address and there is no hard evidence tying you to it.
5. Western union money with fake names and addresses and stuff obviously
The only trace to you is obviously the substance but if you dont' have it at your place either theres really nothing tying you to anything. It really isn't that easy to get a warrant and borrowing other peoples internet with a computer that you don't have at your residence will make it impossible to tie stuff to you. It sounds pretty secure, any other ideas? His idea seems very good, and anyone that is too lazy to go the extra 100 miles should also remember the consequences that can happen. All I know is if I was doing this stuff. I would make sure I had every i dotted and t crossed lol.