Multiple Zend_Mail configurations in application.ini
mail_config.mail_test.transport.type = smtp
mail_config.mail_test.transport.host = "smtp.example.com"
mail_config.mail_test.transport.auth = login
mail_config.mail_test.transport.username = myUsername
mail_config.mail_test.transport.password = myPassword

mail_config.mail_test.defaultFrom.email = john@example.com
mail_config.mail_test.defaultFrom.name = "John Doe"
mail_config.mail_test.defaultReplyTo.email = Jane@example.com
mail_config.mail_test.defaultReplyTo.name = "Jane Doe"

<?php

class Application_Service_MailSettings extends Zend_Application_Resource_Mail { }

// get the bootstrap, so we can get mail_config options
    $bootstrap = $this->getInvokeArg('bootstrap');
    $options   = $bootstrap->getOption('mail_config');

    // initialize the resource loader with the options from mail_config.mail_test
    $mailSettings = new Application_Service_MailSettings($options['mail_test']);
    $mailSettings->init();  // call init() so the settings are applied

    // now the default transport, from, and reply to are set using mail_config.mail_test options.

    // to use a different set of options, just do
    // $mailSettings = new Application_Service_MailSettings($options['other_config');