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Setting CanIt to Allow Listserv Mail

Since listserv-generated messages often displays some properties of mass-generated spam, they are at risk of being blocked. For example, listserv distributed mail appears to come from one user (the poster) when the routing of the mail indicates the mail is originating from some other (often totally unrelated) mail server.

To reduce the number of false positives, it is recommended that you add the hosts for any listservs to your Permit List in CanIt Pro.

Identify the IP Address of Listserv Host

The listserv host is the computer that distributes the mail to listserv members.

  1. Obtain the listserv Host Name
    1. Open a message from the listserv.

      Figure 1-1: A mail from a listserv
      Figure 1-1

    2. The address in the From: field is the e-mail address of the listserv. (In Figure 1-1, this is netoutages@lists.niu.edu.) Note: for some lists, the listserv address will appear in the To: field and the original sender will be listed in the From: field.
    3. An e-mail address is a combination of [account]@[hostname]. So, everything after the "@" symbol is the host name. Copy this host name down. (In Figure 1-1, the host name would be "lists.niu.edu".)
    1. Select the Windows Start button.
    2. Select Run... from the menu.
    3. Type cmd in the Open box. A command prompt window will open.
    4. At the C:\> prompt, type "nslookup [Your Listserv Host Name]" (without the quotes, where [Your Listserv Host Name] is the host name obtained from above) and press Enter.
    5. The nslookup results will then display. (See Figure 1-2.) Look for the section relating to the hostname provided. (In Figure 1-2, the host name "lists.niu.edu" resolves to the IP address of "131.156.69.43". Copy this address down.

      Figure 1-2: Using nslookup
      Figure 1-2

Add the IP Address to the CanIt Permit List

  1. Log in to CanIt with your AccountID (lower case) and network password at http://www.canspam.niu.edu .
  2. For those who use the Simplified Interface select the button for Permit lists, Block lists, etc. to access the Rules link needed to trust a host IP Address. (Note: Advanced Interface users of CanIt can skip this step.)
  3. Select the Rules link to display the rules sub-menu. A new set of links will be displayed.
  4. In the Rules submenu, select the link for Hosts. This will display the Host options. 
  5. In the box labeled Enter a specific IP address:, enter the IP address for the listserv host. (For example, it was earlier determined the IP address of the listserv host [lists.niu.edu] for the NetOutages listserv [netoutages@lists.niu.edu] is 131.156.69.43 .) When the address has been added, select the Add Rule button.
  6. In the picklist for Action, select Always Allow. Add the host name in the Comment field so this rule is easy to identify in the future. Select the Submit Changes button.
  7. The rule should appear (along with any other Host rules that have been established). Log Out.

Once the IP address of a listserv host has been added, all mail coming from listservs from that host will not be scanned by CanIt. This means that if there are more than one listservs from the same list host, the listserv host only needs to be added to the permit list once.

Why must the listserv host be added and not the listserv itself?

It would be much simpler to add the address of the listserv itself to a CanIt permit list rather than identify the listserv host and then determine an IP address. However, some listservs format the messages to appear to be coming from the original poster to the listserv. For listservs of this type, adding the listserv address to the permit list will not actually do any good. in order to function, the individual address of each poster to the list would need to be added. Since this would be an unmanageable effort, it is clearer to permit only the computer routing the listserv messages.

Wouldn't it be even easier to add the entire domain to a permit list?

Yes, this would be an easier solution, but not a very effective one. Many spam type mailings (particularly the more nasty ones such as those used to spread e-mail based viruses) "forge" their mail headers to appear to originate within a particular domain. By permitting an entire domain, all of these type mails would bypass CanIt. Using domains for CanIt permit lists is like cutting big holes in a fishing net. It is not recommended that domains be added to permit lists. This is also true for the "niu.edu" domain.

How does this process effect false negatives?

"False negatives" are messages that are obviously spam that CanIt does not identify. This process is the equivalent of "trusting" the computer that is responsible for the listserv. Spam that makes its way to the listserv will them make its way to all recipients. Listservs that are historically subject to spamming may not be good candidates for this procedure.

More information regarding CanIt can be found at the CanSpam @ NIU.