Simple Golang SMTP relay/proxy server

Topics
#golang #proxy-server #smtp-server #smtp-relay #ssl #load-balancer

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.github 843c02aa0e build(deps): Bump github/codeql-action from 3.29.3 to 3.29.4 2 일 전
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README.md 2358b735b1 Add badge for OpenSSF scorecard (#181) 5 달 전
SECURITY.md 687c793203 Create SECURITY.md (#175) 5 달 전
auth.go 7f34fcbc99 gofmt: Fix formatting 4 년 전
auth_test.go 7f34fcbc99 gofmt: Fix formatting 4 년 전
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go.sum 8f12438b5a build(deps): Bump golang.org/x/crypto from 0.39.0 to 0.40.0 2 주 전
logger.go 441a53cfd9 Fix code formatting with gofmt -s 4 년 전
main.go cafbc78e74 set transient response code on potential temporary error conditions 2 달 전
main_test.go 7f34fcbc99 gofmt: Fix formatting 4 년 전
remotes.go ee8a5dd989 Fix code formatting 2 년 전
remotes_test.go 875264837e add test coverage for scheme validation 3 년 전
smtp.go 085052b96a smtp: ignore HELO error in QUIT 1 개월 전
smtprelay.ini 51ed156dad Remove cmd/hasher for bcrypt. 1 개월 전

README.md

smtprelay

Go Report Card OpenSSF Scorecard

Simple Golang based SMTP relay/proxy server that accepts mail via SMTP and forwards it directly to another SMTP server.

Why another SMTP server?

Outgoing mails are usually send via SMTP to an MTA (Mail Transfer Agent) which is one of Postfix, Exim, Sendmail or OpenSMTPD on UNIX/Linux in most cases. You really don't want to setup and maintain any of those full blown kitchensinks yourself because they are complex, fragile and hard to configure.

My use case is simple. I need to send automatically generated mails from cron via msmtp/sSMTP/dma, mails from various services and network printers via a remote SMTP server without giving away my mail credentials to each device which produces mail.

Main features

  • Simple configuration with ini file .env file or environment variables
  • Supports SMTPS/TLS (465), STARTTLS (587) and unencrypted SMTP (25)
  • Checks for sender, receiver, client IP
  • Authentication support with file (LOGIN, PLAIN)
  • Enforce encryption for authentication
  • Forwards all mail to a smarthost (any SMTP server)
  • Small codebase
  • IPv6 support