This error arises when the IMAP server rejects the connection made by the email application. Possible causes for this issue are a service downtime, an IMAP configuration issue, firewall restrictions, or the requested port is not open.
Check whether the IMAP server and the ports are accurate. For IMAP, the ports are either 143 or 993. Using "nmap" or "netstat," confirm the port you are using is open. Double-check the firewall software on the web or the email server to see whether the firewall is causing this problem.
To determine the root course of the problem, you can check the server and the email logs.
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