smtp4dev is not available for Linux but there are a few alternatives that runs on Linux with similar functionality. The best Linux alternative is FakeSMTP, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to smtp4dev and three of them are available for Linux so hopefully you can find a suitable replacement. Other interesting Linux alternatives to smtp4dev are Origami SMTP (Free, Open Source) and LunaticSMTP (Free, Open Source).
FakeSMTP is a Free Fake SMTP Server with GUI for testing emails in applications easily. It is written in Java. Configure your application to use "localhost" as your SMTP server, and all emails will be intercepted and displayed in this software.
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.
LunaticSMTP is a dummy SMTP server with desktop GUI for testing email sending applications. To use it, start LunaticSMTP and configure your application to use 'localhost' as it's SMTP server. Now it will catch messages sent to it and allow you to view them.