I have set up outbound mail and individual mails go fine. But I can't get the CiviMail working to a group. All the members bounce with a Syntax error. I am running CiviCRM 4.7.22 on WordPress 4.8.2. I've included addresses to recipients on different servers so don't think its a remote problem. The Syntax bounce is supposed to indicate an SMTP transaction error, but things work fine when its just a single email to one of the same contacts.
I have seen other SE posts that might relate, but they are with different configurations CiviMail not sending mails in 4.7.6 / Drupal 7 "DB Error: syntax error" and help on wordpress for send mailling