Its a little heavy handed but you can make your own email relay using a Raspi Pi (or any working computer that can connect to the internet) then installing an email server such as Citadel. But you'll also need to have a website to receive emails, then you'll have to set up configurations.
Pros:
have your own email relay because fuck huge companies
mail is sent and received securely then stored in your server, only you have access to those emails, so no corporations snitching on you when the time arrives
send mail from any custom address, works well with Social Engineering Toolkit
if using Citadel as your email server, account creation takes 10 seconds, plus it features a full chatroom with extra options
make sockpuppet accounts faster (alternatively, just use guerrillamail)
learn a lot about website development and dns
run alongside apache2 or nginx
Cons:
costs money if you want maximum effeciency
requires a static ip address, alternatively use noip or any other dynamic dns software
emails sent to the outside world will be sent to spam folders unless you jump through 5000 hoops
requires https/ssl if you want truly secure mail delivery but thats to be expected