Go-Guerrilla is described as 'A lightweight SMTP server written in Go, made for receiving large volumes of mail. To be used as a package in your Go project, or as a stand-alone daemon by running the "guerrillad" binary' and is an website in the Office & Productivity category. There are five alternatives to Go-Guerrilla, not only websites but also apps for a variety of platforms, including Linux, Mac, Windows, BSD and Self-Hosted solutions. The best alternative is Postfix, which is both free and Open Source. Other great sites and apps similar to Go-Guerrilla are MailHog (Free, Open Source), OpenSMTPD (Free, Open Source), Inbucket (Free, Open Source) and Lettre (Free, Open Source).
Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail. It attempts to be fast, easy to administer, and secure. The software is also known by its former names VMailer and IBM Secure Mailer.
MailHog is an email testing tool inspired by MailCatcher, but easier to install. - Configure your application to use MailHog for SMTP delivery - View emails in the web UI, or through JSON API - Release messages to real SMTP servers for delivery
OpenSMTPD is a FREE implementation of the server-side SMTP protocol as defined by RFC 5321, with some additional standard extensions. It allows ordinary machines to exchange e-mails with other systems speaking the SMTP protocol.
Need to test your webapps outbound emails with Mailinator but stuck behind a firewall? Want to keep the new application you are developing secret until it’s time to release it? Need to validate that emails go out as part of your integration test suite?