We have the same issue when connecting to Exchange SMTP. Tried on ports 25, 465 and 587 - Port 25 is the only port that tries to make a connection. All other ports fail with “Unable to connect to remote server”. We have other clients such as SQL DB Mail and Tableau server which are able to connect fine on port 25… I think this may be due to our SMTP mail server running a self-signed SSL certificate??