SMTPServerDisconnected When Sending via Flask-Mail on Gunicorn I was using .flaskenv for Flask variables and .env for non-Flask variables and Gunicorn doesn't load in .env by default so I added it to a gunicorn.conf.py file without changing any code and it worked as expected now.
SMTPServerDisconnected When Sending via Flask-Mail on Gunicorn mail is created in my create_app() function when the Flask app is initiated. If that were the problem, I wouldn't be able to send email when not running outside of Gunicorn & I believe Flask-Mail handles all connectivity establishment.
