Mail Relays, Transactional SMTP & Privacy Mail

Proton Mail Ingress (mail.proton.me)

Tuta Secure Mail Edge (app.tuta.com)

Fastmail Mail Server (mail.messagingengine.com)

Google Relay Gateway (smtp.gmail.com)

Outlook 365 Cloud Endpoint (outlook.office365.com)

Postmark Transactional SMTP (smtp.postmarkapp.com)

SendGrid Transactional API/SMTP (smtp.sendgrid.net)