harakahog

Mailhog behind Haraka for STARTTLS

Problem statement

For QA purposes there is a need for a mailcatcher service that supports TLS. MailHog doesn't.

Solution

Let us configure Haraka to operate behind a proper MTA that is capable of supporting STARTTLS in a secure manner. Specifically, we will configure Haraka to:

• utilize TLS encryption
• only accept inbound relay connections from a pre-approved whitelist of IP addresses
• use SMTP LOGIN auth solely over TLS
• forward all received emails to the companion MailHog container within the same Docker Compose environment.

For this proof-of-concept, we will be using Docker Compose, although a Helm chart would also be a viable option.

To configure

I'm proposing an approach that combines two types of relay authorization: IP ACL and SMTP user LOGIN type authZ.

Also, system will need some key and certificate.

Prepare key and certificate

Run

openssl req -newkey rsa:2048 -nodes -keyform PEM -keyout tls_key.pem -outform PEM -x509 -days 365 -out tls_cert.pem

and answer certificate questions. Make sure that generated files are in h-config dir and h-config\tls.ini file is pointing at them.

For commercial, non-self-signed certificate, one needs to construct a certificate chain file.

Prepare user credentials

Edit h-config/auth_flat_file.ini and add some user with password there.

Configure IP address ACL

If you want to enable IP address controller relay, add IP/range in CIDR notation to h-config/relay_acl_allow. One entry per line.

As an example - values for localhost and for MacOS docker internal network are already there.

To run

docker compose up

When run, there will be some files created in h-config, most notably dhparams.pem file and me server identity file.

To test

SMTP over telnet is not that complicated but let's use swaks (https://github.com/jetmore/swaks) on MacOS.

brew install swaks

And then let's send some test email

swaks --from [email protected] --to [email protected] --server localhost:587 -tls -a LOGIN

-tls option forces STARTTLS communucation. -a LOGIN forces LOGIN SMTP auth.

Remember that haraka proxy is configured to allow relays from given whitelisted IP or after successful auth.

See the mailhog web ui (http://localhost:8025) to see received emails.