Apple Mac OS X Server (Administrator’s Guide) - Manual (Page 399)

Mail Service 399
Enter a single IP address, such as 192.168.123.55.
Enter an IP address range, such as 192.168.40-43.*.
Enter an IP address/netmask, such as 192.168.40.0/255.255.248.0.
Enter a host name, such as mail.example.com
Enter an Internet domain name, such as example.com
5 Optionally select “Log recipient rejections to error log.”
6 Click Save.
Rejecting SMTP Connections From Specific Servers
Your mail service can reject all SMTP connections from servers on a disapproved-servers list
that you create. No one can authenticate from a disapproved server, much less send your
users mail or relay mail through your mail service.
To reject SMTP connections from specific servers:
1 In Server Settings, click the Internet tab.
2 Click Mail Service and choose Configure Mail Service.
3 Click the Filter tab.
4 Select “Reject messages from SMTP servers in list” and then edit the list of servers.
Click Add to add a server to the list.
Click Remove to delete the currently selected server from the list.
When adding to the list, you can use a variety of notations.
Enter a single IP address, such as 192.168.123.55.
Enter an IP address range, such as 192.168.40-43.*.
Enter an IP address/netmask, such as 192.168.40.0/255.255.248.0.
Enter a host name, such as mail.example.com
Enter an Internet domain name, such as example.com
5 Click Save.
Checking for Mismatched SMTP Server Name and IP Address
Your mail service can log and optionally reject connections from a server whose DNS name
doesn’t match the name that your DNS service gets when it looks up the server’s IP address.
This method intercepts junk mail from senders who pretend to be someone else, but may
also block mail sent from a misconfigured SMTP server.