- You run the risk of hardware failure, which would take days to recover. When your warranty expires, it'd cost you, too.
- Disk failure may lose all your data.
- Fire, theft, or hurricanes may destroy it.
- You still give access to your data to a company, which controls software updates and the EC2 proxy (in this case).
- Many home ISPs have shitty upload connectivity, so your email won't work that well on the go.
- Internet and power outages mean you won't send or receive any email.
- You lose the knowledge email providers get from scale, including ever-evolving spam filters, and a guaranteed clean outgoing IP.
If you really want to control your data, just spin up something like ownCloud (not sure if that's the best solution, just an example). Companies like DigitalOcean make it as simple as point and click.