I'm trying to troubleshoot a problem in which email sent to a mail-enabled distribution list (DL) doesn't reach all users. What should I look at first?
Begin by identifying which users aren't receiving the email messages. This process is easy for small DLs but can be tricky for larger ones. (My guess is that users who don't get a particular message will complain, making your task somewhat easier.) If you use Microsoft Exchange Server 2003, the message-tracking logs will contain specific entries for message delivery to each DL recipient. You can easily determine who didn't get the messages by reviewing these logs. Then, determine whether any patterns exist to the missing messages. For example, if all the users who aren't receiving the message have mailboxes on the same server, your problem likely relates to that server.
—Paul Robichaux