Send e-mail only to users related to entry with Postmaster/Sprout I would like to set up Postmaster or Sprout Email to send an e-mail notification when a new entry is added. I only want the email sent to users who are linked to the entry via a custom field (type:user).

I've having trouble solving this without writing a plugin to extend either plugin. If I have to write a plugin to do this, any tips? Otherwise, how can I do this with either plugin?

To reiterate:

How can I have notifications sent only to users who are linked to the new entry via a custom field (type:user)?
If I'm correct in thinking that you want users who have been added to a relation field on an entry to receive an email, then the following will work.

You will have to write a plugin to listen for the onSaveEntry event. You can then loop through any users added to the custom field of the entry and send them an email.

The code would look something like the following:

craft()-&gt;on( 'entries.onSaveEntry', function( Event $event ){

    $entry = $event-&gt;params['entry'];
    // The users field returns user id's
    $userIds = $entry-&gt;getContent()-&gt;users;

    // Grab the user models using the id's from the entry field
    $criteria = craft()-&gt;elements-&gt;getCriteria( ElementType::User );
    $criteria-&gt;id = $userIds;
    $users = $criteria-&gt;find();

    // If we have users
    if ( $users ){
        // For each user
        foreach ( $users as $user ){
            // Builds and sents the email
            $email = new EmailModel();
            $email-&gt;toEmail = $user-&gt;email;
            $email-&gt;subject = "You've been added to an entry";
            // Use this for a plain text email body
            $email-&gt;body = '';
            // This uses a html body from a twig template, you can pass the entry to it to access the entries fields
            $email-&gt;htmlBody = craft()-&gt;templates-&gt;render( 'pluginname/_emails/email-template-name', array(
                'entry' =&gt; $entry
            ) );
            craft()-&gt;email-&gt;sendEmail( $email );
        }
    }
});