This module allows for SMTP configurations on a per email key basis by replacing the implementation of smtp's mail backend plugin. It requires the smtp module.

Use the project's settings.php or settings.local.php to add SMTP configurations
keyed by the email key like so:
<?php
$settings['smtp_multiple_config']['email_key']['smtp_host'] = 'smtp.gmail.com';
$settings['smtp_multiple_config']['email_key']['smtp_port'] = '465';
$settings['smtp_multiple_config']['email_key']['smtp_protocol'] = 'ssl';
$settings['smtp_multiple_config']['email_key']['smtp_username'] = 'user@gmail.com';
$settings['smtp_multiple_config']['email_key']['smtp_password'] = 'pass';
$settings['smtp_multiple_config']['email_key']['smtp_from'] = 'user@gmail.com';
$settings['smtp_multiple_config']['email_key']['smtp_fromname'] = 'Me';
?>

Alternatively use the hook_smtp_multiple_config_alter() hook:
<?php
function my_module_smtp_multiple_config_alter(array &$config, $key) {

if ($key === 'comment_notify_comment_notify_mail') {
$config['smtp_host'] = 'smtp.gmail.com';
$config['smtp_port'] = '465';
$config['smtp_protocol'] = 'ssl';
$config['smtp_username'] = 'user@gmail.com';
$config['smtp_password'] = 'pass';
$config['smtp_from'] = 'user@gmail.com';
$config['smtp_fromname'] = 'Me';
}
}
?>

Short name
smtp_multiple
Supporting organizations
Responsible for creation and maintainership of the project.