Not too much, unless you are completely new to server environments and networking. You'll likely experience security breaches rolling your own crypto unless yo

Not too much, unless you are completely new to server environments and networking. You'll likely experience security breaches rolling your own crypto unless you are an expert in cryptology. You'll also experience security breaches running your own email server if you also don't know what you're doing, but it's far easier to learn what it takes to configure an email server correctly from a security perspective than rolling your own crypto. The bigger problems with running your own email server is NAT/CGNAT, ISP restrictions, and the fact that the big players will still ignore you due to only caring about the other big players.