SMTP Worker

Send queued e-mail in separate process through a JSON abstraction.

Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.

Why?

• Security, SMTP credentials are isolated from the website
• Simplicity, the website creates JSON and all SMTP logic is isolated here
• Scalable, things need to go faster? Start a second..third..fourth.. worker!
• Cleaner, no more ugly timeouts in the browser if trouble and no more lost emails/customers!

How?

• Use Beanstalkd (http://kr.github.io/beanstalkd/) to add jobs in a queue.
• One or more SMTPw-instances read the queue and try to send
• Failure? Wait 5sec on SMTPw error or wait for Beanstalk deadline (if process got killed) and try again!

Config

{
	"beanstalk": "127.0.0.1:11300",           // Hostname:port to Beanstalkd
	"from": {
		"support": {                            // From in JSON matches to this from
			"user": "emailuser",                  // SMTP username
			"pass": "supersecretpass",            // SMTP password
			"host": "smtp.yourcompany.com",       // SMTP hostname
			"port": 1234,                         // SMTP port
			"from": "support@yourcompany.com",    // From-address (used in mail header)
			"display": "RootDev",                 // Display-name added before From-address
			"bcc": [
				"alwayssendhere@yourcompany.com"    // Send a secret copy (can be useful for monitoring/debugging)
			],
			"allowBCC": false                     // true to allow the BCC-field to be appended by the Email-struct
		}
	}
}

Be careful with Insecure=true as it will allow MITM (Man In The Middle Attacks)

Bounce sets the From-header to the bounce-address and sets Reply-To for human replies.

Usage

./smtpw -h
Usage of ./smtpw:
  -c="./config.json": Path to config.json
  -s=false: Delete e-mail on deverr
  -v=false: Verbose-mode

• Path config.json, where to find the config.json file
• Delete on deverr, delete and flush the e-mail content if JSON is invalid.
• Verbose-mode, log what we're doing

JSON

type Email struct {
	From        string          // Key that MUST match From in config
	To          []string
	BCC         []string        // Only used when allowBCC=true in config
	Subject     string
	Html        string
	Text        string
	HtmlEmbed   map[string]string // file.png => base64(bytes)
	Attachments map[string]string // file.png => base64(bytes)
}

WARN: I like my parsers strict. Every HtmlEmbed key is scanned with Html.contains(cid:key) and if not found it will throw an error.

WARN: Invalid supplied email-address will fail with errors like mail: no angle-addr, please use a descent email RFC validator, i.e. for PHP https://github.com/iamcal/rfc822

Errors

panic: dial tcp 127.0.0.1:11300: connection refused Install Beanstalkd and update config if Beanstalkd is running elsewhere?

x509: certificate signed by unknown authority Your SMTP-server has a self-signed certificate? Time to get a signed one!

Job never received by SMTPw? Is the job sent to the email tube? As smtpw only listenes to this tube.

telnet 127.0.0.1 11300
use email
peek-ready << should show your JSON here

Systemd

# User + systemd
useradd -r smtpw
mkdir -p /home/smtpw
vi /etc/systemd/system/smtpw@.service
vi /etc/systemd/system/smtpw.target

chmod 644 /etc/systemd/system/smtpw@.service
chmod 644 /etc/systemd/system/smtpw.target

systemctl daemon-reload
systemctl enable smtpw@1
systemctl enable smtpw@2

systemctl start smtpw@1
systemctl start smtpw@2

External deps

• https://github.com/go-gomail/gomail
• https://github.com/maxid/beanstalkd