Mailer table and smart host routing for outgoing messages

After processing an outgoing message, Conbool by default delivers straight to the recipient's mail server. The mailer table overrides that behaviour and routes the outbound path to a defined smart host. The typical reason is a downstream instance for security, archiving or backup that is to stay in the path.

When this is worth it

Without smart host routing an outgoing message leaves Conbool directly towards the internet. An existing outbound security or archiving instance would be bypassed. Smart host routing keeps that instance in the path while Conbool continues to apply disclaimer, signature or encryption.

Structure of the mailer table

The mailer table is a text list. Every line consists of a key and a target, separated by a space or a tab. Lines starting with # are comments.

Possible keys are:

• an exact recipient domain such as example.com
• a subdomain branch with a leading dot such as .example.com, which covers the domain and its subdomains
• a single address such as person@example.com
• a catch-all rule with * or @, which covers all remaining recipients

The target is a smart host in the form esmtp:[host]. smtp: and relay: are permitted as well. If more than one line matches, the most specific one wins. The order is address before domain before subdomain branch before catch-all rule. The smart host accepts the messages on the standard SMTP port.

Example

All outgoing messages to the smart host of a security instance:

# Catch-all rule: everything to the smart host
*  esmtp:[smarthost.example.net]

Redirect only a single recipient domain, everything else goes the regular way:

example.com  esmtp:[relay.example.com]

Activation

The mailer table is stored in the tenant settings and loaded as a file. Access is governed by a dedicated permission and reserved for the routing area. After saving, the table applies to the outgoing messages of the managed domains.

The outbound path itself is routed to Conbool through the Exchange connectors. How rules treat outgoing messages in terms of content is shown in signing and encrypting outgoing messages and in rules and assignment in Disclaimer.