Hi,
I tried, it didn’t solve.
I installed Postman, which gave me and Error 500 upon activation with “PostmanWpMailBinder: wp_mail is already bound, Postman can not use it” in the logs. I couldn’t solve it, even with Debug plugin (which didn’t give me error.log)
I tried WP Mail SMTP and WP Mail Bank. Although they are working fine, I got the same red box.