Cannot open connection
Your email (SMTP) server is unable to start an SMTP session. Typical replies will be "SMTP Error 101, Error opening connection" or "SMTP Error 101, cannot open SMTP stream". All SMTP Error 101 errors usually point to a configuration problem, such as an incorrectly spelled SMTP server, or an IP address that does not exist, or an SMTP port that does not exist or which the recipient will not accept SMTP connections on, or some other process is already using the configured SMTP port.
Realistically, there are a few possibilities for the error. You'll need to research each possibility for the error and act accordingly.
SMTP Error 101, Error opening connection
SMTP Error 101, cannot open SMTP stream