Mailpit is a multi-platform email testing tool and API for developers, inspired by MailHog but much faster. It runs entirely from a single binary with no installation required and features an SMTP server, web UI to view emails, advanced mail search, message tagging, and configurable automatic email pruning. Mailpit can also act as a substitute for sendmail and offers optional browser notifications, SMTP relaying/message release, SMTP authentication, HTTPS for web UI, and basic authentication for web UI. It is faster than MailHog and performs better with large amounts of emails or processing emails with attachments. The API of Mailpit transmits less duplicate and unnecessary data, and there is HTTP compression.
https://github.com/axllent/mailpit