Very interesting, I disabled Paypal for Woo, using the default Paypal gateway and the checkout process was fine and returned our test customer to the website with the order received confirmation, however, right in the middle of the page is that WP-SES error.
So it appears there might be a conflict in the chain between Woocommerce and WP-SES or just an error with WP-SES. I’ve reached out to them for help as well.
Thanks.
On the WP-SES forums, the developers said this is generally an issue with another plugin making a call to modify pluggable.php/wp_email() because their plugin does that.
I deactivated all other plugins except for woocommerce, and paypal for woocommerce first. Everything worked as expected. I enabled WP-SES and had the header issue.
I thought it might be Paypal Express because that’s the last user action before the error occurs.
