Papercut is a simplified SMTP server designed to only receive messages (not to send them on) with a GUI on top of it allowing you to see the messages it receives.
Papercut vs FakeSMTP opinions
Very good GUI on windows with a lot of configuration options and viewable headers etc.
Should be rated a lot higher. Excellent free alternative to Mailtrap
Windows native app with helpful message rendering.
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.
MailCatcher runs a super simple SMTP server which catches any message sent to it to display in a web interface. Run mailcatcher, set your favourite app to deliver to smtp://127.0.0.1:1025 instead of your default SMTP server, then check out http://127.0.0.
Dummy SMTP server that sits in the system tray and does not deliver the received messages. The received messages can be quickly viewed, saved and the source/structure inspected. Useful for testing/debugging software that generates email.
Pacomail is a test mail server solution that allows testing email without sending them to the real users of your application. Code, preview, test, and collaborate using a development tool designed for email.
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.