Email to Distribution List doesn't "go".

For the last year I have emailed myself and Blind Copied to a distribution
list. I do this 4 times to 4 different lists. I am using Outlook 2003. I
normally get the emails and my contacts get it. This month I did not get
the emails to myself which threw up a red flag. I've done a small survey of
the intended receipients and most did not get the email. I did have one guy
say he got all of my attemtps. My distribution lists have approximately 95
members and only their names and email's are entered in the contact
information. I contacted my service provider and they checked my settings
and said they're OK. I can send and receive emails. I contacted Norton to
see if there might be a problem with protection stuff; we removed the
software, tested it, then put it back. It doesn't appear to be the problem.
Out of the 350 contacts on the 4 lists, about 3 "came back" with an error.
Any suggestions on why most of this emails did not go through.