PigMail is a transactional email service built for people - not large corporations. Most transactional email services require that you be registering as/for a company. This is because an email service lives and dies by its reputation.
The ways to try to protect their reputation include:
PigMail approaches the problem from the accountability perspective, by utilizing a reputation system. You cannot sign-up on your own - you must be invited by an existing member that has a sufficiently high in-system reputation. If you send spam, you are thrown out of the network, and the reputation of whomever invited you suffers.
Using this method, we're able to maintain a high network reputation, without immediately reaching for your wallet or business credentials. In fact, you can use our service entirely anonymously, with access via the onion network, and no personally identifiable information stored besides your credentials. Furthermore, because we're focusing on smaller end groups, we have fairly decent free offerings, and the ramp-up starts small, increasing only as your sending volume does. Take a look at what we've got!