Okay, I have solved this. Wordpress was sending emails just fine, but WooCommerce plugin was not. In WooCommerce > Settings > Email, I had to change the "From address" from email@example.com to firstname.lastname@example.org.
Posts made by mattp
RE: Wordpress WooCommerce emails: Authenticated user cannot send mail as
Wordpress WooCommerce emails: Authenticated user cannot send mail as
I am using Wordpress (Managed) with the WooCommerce plugin. I can successfully send test emails, but WooCommerce is not sending notification emails on test orders, for example new order notifications. I see the error message in the Cloudron email logs:
Connection denied. Authenticated user email@example.com cannot send mail as firstname.lastname@example.org
I do not remember changing any of the default email configurations, but I suppose I did something since I am getting this error.