Under 'Mail Server' tab:
We usually just put the local LAN IP address of the SBS/Exchange server in the 'Mail Server' box, then create a reply address e.g. [email protected] as the reply address (assuming that the 3CX and mail-server are on the same LAN???).
We don't usually need to input an SMTP username & password for an exchange server ...
Under 'E-mail Notifications' tab:
We create a mail-group in Exchange and use that for the e-mail address input at the top of this page. We can then control distribution of 'Event' messages to customer IT staff as well as ourselves (as the system supplier and maintainer), via the Exchange mail-group and active directory.