Cannot connect to Exchange server

If you're aware that your exchange server is in fact using Office 365, you should instead select "Office 365" from the Server Type dropdown when adding a new account. This should help with discovery.

Note, that if the Hide Mailbox from Address List option is enabled in your Exchange accounts settings (you can verify this by logging into your online exchange account), this would prevent BusyCal from discovering your account. Please ensure this is disabled as this is a common cause of connectivity failures.

If in doubt, ask your account administrator for the exact server connection address. This would be something like "https://myserver.com/EWS/Exchange.asmx". Enter this into the Internal Server address field when entering account information.