Connection refused or inability to open an SMTP stream
This error is typically referencing a connection issue to the remove SMTP/Mail server. Often in relation to firewalls or misspelled domains.
As in most cases, you'll want to ensure that the email address being sent to is spelled correctly (especially the domain name in this case). Upon confirming that is correct, attempt connecting to the remote SMTP server from a local machine (computer) other than your server to see if you are able to connect to that server. If you are unable to connect from your local machine it's most likely an unresolvable issue at the remote (recipient) email server.