Mailtrap is a fake SMTP server for development teams to test, view and share emails sent from the development and staging environments without spamming real customers.
Mailtrap vs smtp4dev opinions
smtp4dev is a local system, mailtrap is an online service
Email Testing for QA & Development Teams. Catch every email your product sends, analyze it's contents, follow links and test deliverability all via the Mailosaur API.
Ethereal is a fake SMTP service, mostly aimed at Nodemailer users (but not limited to). It's a completely free anti-transactional email service where messages never get delivered.
Origami SMTP was created with the idea to have a fake email server for testing purposes that supported TLS. This is because the code the developer was working on at the time had several hard coded values enforcing TLS so most other solutions would not work.
Origami SMTP vs smtp4dev opinions
Cross-Platform with TLS support.
QA tool for automating end-to-end email tests. Get unlimited private email addresses and inboxes for testing new user signups, transactional emails and drip campaigns, deliverability and spam scores, etc. Integrates with your CI/CD workflow. Includes spam testing.