Glossary
What is email authentication?
Email authentication is how a receiving mail server checks that a message really came from the domain it claims. SPF and DKIM are the records you publish in your DNS to prove it. Connect your sending domain and portal email passes those checks, which is what keeps it out of spam folders.
Still deciding
See the terms as features
The glossary explains the vocabulary. The features page shows what each of these looks like in a portal you run yourself, and the pricing page shows what it costs.