From header can cause send email to fail

First, don't know how relevant it is but I am running the smtp module and using gmail.

In the _watcher_email_notifications_send_message function, this line causes my site to fail to send email:

$from = sprintf('%s <%s>', $site_name, $site_mail);

The error reported is this, which suggests it has somehow not parsed the from name and address properly.

Error sending e-mail from "SiteName" to xxx@yyy.com: The following From address failed: "SiteName"

This fixes it, and emails are still received with a distinct from name and email address. I am unsure if this is default behaviour, or the smtp module is determining the from name after the fact.
$from = $site_mail;