CoSE IT hosts several mailman mailing lists on lists.ps.isu.edu
lists.ps.isu.edu uses a technique called greylisting to reduce spam. It keeps track of a three pieces of information about each mail, sending IP address, sender email, recipient email. The first time the server encounters a new combination, it delays delivery for 1 hour. It denies the request the first time, but correctly configured email servers retry in an hour and the server has now seen this combination before, and accepts the mail. Many spambots are not correctly configured email servers, and don't retry. What it means to you the first time you send an email to a new list, or from a new IP (home IP's are sometimes dynamic, and may change each time) your mail may be delayed one hour. Subsequent mail sent from the same IP to the same recipient (in this case the mailing list) is not delayed.