It's difficult to say what's happening without having admin access to the server. Even then, one would have to scan the logs for this individual request and there may not be a clear explanation.
I have one question. If using 'wget', does your cron command contain the "-T 0" paramater? Without this paramater it can be possible for wget to 'reload' the dailymail page after a certain amount of time. This results in dailymail being loaded twice at the same time, in parallel. It's particularly disastrous because users not yet processed from the first mailing will be included in the second mailing and processed twice, resulting in two followups. A similar problem occurs rarely with "KeepAlive On" in httpd.conf or PHP.
Regards
