SMTP Plugins Don't Work with Enfold

Our shared mail server has been flagged as spam by Gmail. All contact form emails are going directly into the Spam folder because of the server. We need to change to SMTP to avoid this happening. I have tried three different SMTP plugins and all of them fail. The last one I tried was Wp-Mail-SMTP. It displayed a failed report but I’m not understanding why it’s failing. All Gmail settings are correct as well as email and password.

Part of error message:
[“authenticate”]=>
string(35) “SMTP Error: Could not authenticate.”
[“connect_host”]=>
string(43) “SMTP Error: Could not connect to SMTP host.”
[“data_not_accepted”]=>
string(30) “SMTP Error: data not accepted.”

I’m running WP 4.2.5, Enfold 3.2.3.

Thanks for any insight into the issue.