Simple Golang SMTP relay/proxy server

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

Bernhard Froehlich de005d41a4 Bump version to 1.3.0 6 éve
.drone.yml 2c9645ac68 Add drone config 6 éve
LICENSE c707438ae8 Update MIT license template 6 éve
README.md ade7cbca36 Rename to smtprelay 6 éve
auth.go d11f8d81ea Fix formatting 6 éve
config.go 21b597f351 Bump version to 1.3.0 6 éve
go.mod 5f82b4736c Update dependencies 6 éve
go.sum 5f82b4736c Update dependencies 6 éve
main.go 0b65e904d8 Allows specify the sender used on SMTP conversation with outgoing server. 6 éve
smtp.go 3a96014c70 Revert package renaming 6 éve
smtprelay.ini 769193ea4d Adjust the description of remote_sender parameter. 6 éve

README.md

smtprelay

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 to GMail without giving away my GMail credentials to each device which produces mail.

Main features

  • 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 (GMail, MailGun or any other SMTP server)
  • Small codebase
  • IPv6 support