This Odoo technical development blog is my way to contribute back to the Odoo Community, for all the selfless and great sharing by the community members.
Recently, when Odoo user sending email with attachment larger than 7MB, which takes more than 60 second, there will be a SMTPServerDisconnected error.
First, i thought it was the nginx issue, and had added the following to the nginx config file, but the problem persisted.
Finally, i've able to find the culprit which is in the <odoo installation folder>/odoo/addons/base/models, and change it to
SMTP_TIMEOUT = 300