In my search of the best encrypted email service, I've settled on Startmail.com as the best encrypted email service for everyday use.
A Sensible Name
Having an email service you can pronounce is important when others ask what your email is. Startmail is not foreign sounding, even though it's in Europe and it's doesn't sound like you're using Edward Snowden's email. Services like Tutanota, Countermail, Riseup, and others have their place, but they don't sound like mail a normal person would use when a semi-professional sounding name may be important.
Startmail has two forms of disposable emails, temporary (random generated) that can expire in an hour or up to two weeks without renewing and ten (active at one time) non-expiring custom disposable addresses. Great for a one-time use or signups you know will be spammed, but need to be valid for registration.
Startmail is able to generate or import your own private key. You are responsible for the passphrase and will need to input the passphrase when encrypting, decrypting and signing emails in the Webmail interface. Unlimited public key storage and automatic use when an associated email address is used. Contact list can have options for Always Encrypt or Always Sign.
Encrypted Without PGP
If your recipient doesn't have a public key (educate them!), startmail is able to encrypt the email using a question and answer. You create the question and answer and the recipient(s) must provide the answer. The email is displayed in the browser with HTTPS and an encrypted reply is able to be composed on the same page. The reply is encrypted with your public key and the passphrase is required.
There is a limit of 5 devices to use imap, each one receives a unique password. Lose a device, delete the password, no worries. Sometimes I've wished for one more, but between a couple of desktops, phone and tablet, if another is needed the webmail interface works anytime. POP3 is not supported. If you're using POP3 for your client email, stop.
Startmail encrypts all of your email at rest and in-transit, even without using PGP. Being based in Holland the privacy requirements are more strict, a Holland court is needed to hand over any information about you. Startmail says they won't read your email, but it doesn't say they can't. In their white paper they say they need two senior team members to decrypt. The white paper is very impressive in their lack of keeping records and even payment information cannot be associated with an account.
In their current terms of service they mention only need to know, NDA's and not third parties. That's for email that is not explicitly encrypted with your private key. If email (or anything) is encrypted with your private key, only a brute force dictionary attack on your passphrase will decrypt your message.
This page has more detail about their security and the information they keep (not much) and for how long (not long). Even without taking bitcoin, if the payment company is independent and cannot correlate between stored payment information and email accounts, it's almost anonymous.
If you're that much of a target some agency will go to a Dutch court and brute force your passphrase, you're going to be up a creek eventually anyway.
The 7 day trial is limited and doesn't have all of the features enabled like imap. It gives a feel for the interface, but that's about it. I went through two trials before I put up money. It's my everyday email, I love the easy PGP integration, the disposable addresses and the seamless Thunderbird, Enigmail integration. PGP means any program can be used and still be compatible and read in Startmail.
After reading everything I could find, most reviews online are out of date and from someone that used it enough to write a review. After almost a year of everyday use and reading everything on their site documents page, I'm convinced they are the best for anonymous, secure and encrypted email. It's too bad they don't have a really free option, but the price isn't bad and worth it to get away from all of the other big "free" email services. Sometimes "free" costs too much.