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Modules Reference
outbound_smtp_auth

outbound_smtp_auth

Last updated May 2025

This module enables users to specify authentication parameters for a given set of messages so that Momentum will authenticate against the peer server when it sends outbound mail. It currently supports the AUTH LOGIN, AUTH PLAIN and AUTH XOAUTH2 methods of authentication. You can specify the parameters in configuration or in lua, or use a combination of both.

Note

This module makes heavy use of message contexts to facilitate authentication. If it is enabled, you risk having extra I/O unless keep_message_dicts_in_memory is on.

Configuration

This module is refactored in Momentum 5.1, but this feature is available in Momentum 4.2 and later. AUTH XOAUTH2 support is added in 5.1.

Configuration variables are listed below. These values can all be changed and overridden by setting message context variables with the same name as the options in lua. All variables are valid in the binding group, binding, domain, and global scopes.

outbound_smtp_auth_pass

The password or auth token (e.g. for AUTH XOAUTH2) that will be passed to the remote server. It has no default value.

Note

Setting the password in configuration will leave it as plaintext. To set the password more securely, it's recommended to dynamically retrieve it from a data store in lua and set it in the context variable that corresponds to this option.

outbound_smtp_auth_type

Determines what authentication protocol should be used. The only supported values are PLAIN, LOGIN and XOAUTH2. It has no default value.

outbound_smtp_auth_user

The username that will be passed to the remote server. It has no default value.

Usage

A hook outbound_smtp_auth_config(msg) is added by this module to allow per message auth settings. The settings in ec_message context will override the configuration values. This hook is called in delivery/scheduler thread before sending SMTP AUTH command. Please avoid blocking or lengthy operations when implementing this hook.

Basic examples of usage are provided below.

The following example shows how you can extend the new hook and set the username and password in lua for each message.

function mod:outbound_smtp_auth_config(msg)
  --print('NOTICE: outbound_smtp_auth_config Lua hook called');
  msg:context_set(VCTX_MESS, 'outbound_smtp_auth_type', 'XOAUTH2')
  -- credential taken from example here:
  -- https://learn.microsoft.com/en-us/exchange/client-developer/legacy-protocols/how-to-authenticate-an-imap-pop-smtp-application-by-using-oauth
  msg:context_set(VCTX_MESS, 'outbound_smtp_auth_user', 'test@contoso.onmicrosoft.com')
  msg:context_set(VCTX_MESS, 'outbound_smtp_auth_pass', 'EwBAAl3BAAUFFpUAo7J3Ve0bjLBWZWCclRC3EoAA')
end

The following example shows how to use the new configuration variables to set distinct authorization parameters for two different domains.

outbound_smtp_auth { }

Keep_Message_Dicts_In_Memory = true

Domain "messagesystems.com" {
  Outbound_SMTP_AUTH_Type = "LOGIN"
  Outbound_SMTP_AUTH_User = "msys"
  Outbound_SMTP_AUTH_Pass = "msys"
}

Domain "sparkpost.com" {
  Outbound_SMTP_AUTH_Type = "PLAIN"
  Outbound_SMTP_AUTH_user = "sparkpost"
  Outbound_SMTP_AUTH_pass = "sparkpost"
}

Domain "bird.com" {
  Outbound_SMTP_AUTH_Type = "XOAUTH2"
  Outbound_SMTP_AUTH_user = "test@contoso.onmicrosoft.com"
  Outbound_SMTP_AUTH_pass = "EwBAAl3BAAUFFpUAo7J3Ve0bjLBWZWCclRC3EoAA"
}
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