There are only two other options:
1)
-Ideal/common option is to:
-enable your server to accept the mail by running the CEICW ( server management | internet and e-mail | connect to the Internet)
-forward port 25 from your router to the SBS
-have whomever manages your external DNS for your domain create a host record for SBSname.Mydomain.abc which points to your public IP
-have whomever manages your external DNS for your domain create an MX record that points mail fro your domain to your host record for SBSname.Mydomain.abc
2) POP the mail directly from the Outlook mail clients. They can then select to have the mail dropped in a local PST account, or their Exchange server account mail box