This error shows that the mail server is either refusing the connection or is getting timed out. There can be several causes why this is occurring.
Check and confirm whether IMAP is enabled and the port is correct (usually 993) and try the security as SSL over TLS. Try temporarily turning off firewall and anti-virus programs to check whether there is any difference. If not, it is better to check the error logs to determine the cause before solving the issue. You can contact the mail server admin to check the logs to find the root cause for this error and then fix the problem based on it.
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