WooCommerce not sending order processed emails after update

I am having trouble with the email side of this sites store after updating to the latest version of WooCommerce.

The owner uses a Gmail account for all emails and it started flagging up with a "this email may not have been sent by name@gmail.com" but we have also noticed that when he clicks order complete on the woo commerce plugin no emails are being sent to notify his customers that their order is on its way. This is something that worked fine before.

I tried to fix the issues bu using an SMTP plugin (Easy WP SMTP) i filled out the info for Gmail but could not get it to work correctly, so I have disabled that plugin for now