Error: smtplib smtpserverdisconnected Connection Unexpectedly Closed

What's Causing This Error

The cause of this error is the server unexpectedly disconnecting or attempting to use the SMTP instance without connecting it to a server.

Solution - Here's How To Resolve It

If you are not using TLS already, switch to authenticated connection with TLS and ensure the port is 587. And go through the SMTP configurations and check whether you have declared valid variables.

1. SMTP host
2. SMTP port (25, 465, 587)
3. SMTP protocol (587 for TLS)
4. Username and password

Check and re-verify the protocol, the port, and the host.