Relay Blocking

Relay Blocking prevents use of your SMTP server by unauthorized persons. This technique of fighting SPAM (unwanted email) cuts off a delivery method used by many bulk mailers. Many bulk mailers will use an SMTP other than their own to send messages to the internet in an effort to disguise the true source of the SPAM, and to circumvent other filtering means. Mail Server provides a mechanism to prevent this type of relaying.



SMTP IPs.config

The SMTP IPs.config file contains ranges of IP addresses that you are willing to relay mail for. These ranges are typically the IP addresses of the computers on your own LAN that are authorized to send e-mail. You may also want to permit use of the SMTP server by others not on your LAN as well.

For example, the Spider Island SMTP server is configured to accept mail for relay only from computers on our LAN. Specifically the range of IP addresses thru If you do not specify any address ranges in the SMTP IPs.config file, Mail Server will accept mail for relay from any other computer.



What is "Mail for Relay"?

Mail for Relay is any mail that will be routed through Mail Servers "Default" gateway because it has a "To" address that is not in your "Local Domains" list, and not in the "Domains Lists" of any of your Mail Server gateways. In other words, it has to be addressed to a foreign address, not known by your Mail Server.



Editing the SMTP IPs.config File

The SMTP IPs.config file is a tab delimited text file that you can modify with just about any text editor including "Simple Text" or BBEdit. The SMTP IPs.config should be located in the server "config" folder along with "Mail Server.config"


Each record in the file must have the following structure.

record type<tab>starting-ip-address<tab>ending-ip-address<return>

  • The record type for this file is 'ipok'. Enter this without the single quotes. It must be lowercase.
  • Each record, inlcuding the last, needs to have a return at the end of the line.
  • IP addresses must be entered in "dotted-quad" notation like "".

A finished record should look like this.


You can specify a single computer in a record by entering the same starting and ending addresses.

After editing the file, save it, then restart Mail Server to have the changes take effect.