lplightle on "[Plugin: WP Mail SMTP] Test email works, but Gravity Form Notification email does not"

I am having trouble getting Gravity Forms Notification emails to be delivered. They don't even go to spam. I installed WP Mail SMTP and configured it. The test email works great, but the Gravity Forms Notification emails are still not working. Here is the error from the Gravity Forms log file:
2015-08-04 12:05:19 - DEBUG --> GFCommon::send_email(): Result from wp_mail():
2015-08-04 12:05:19 - ERROR --> GFCommon::send_email(): The mail message was passed off to WordPress for processing, but WordPress was unable to send the message.
2015-08-04 12:05:19 - DEBUG --> GFCommon::send_email(): The WordPress phpmailer_init hook has been detected, usually used by SMTP plugins, it can impact mail delivery.
2015-08-04 12:05:19 - DEBUG --> GFCommon::send_email(): PHPMailer class returned an error message: SMTP Error: data not accepted.

https://wordpress.org/plugins/wp-mail-smtp/