[ic] Some emails can't be sent - could this be why ?

[DB]

>> As I said in a previous post, suddenly about one in three of my order 
>> emails don't get sent. The rest arrive normally. According to the 
>> catalog's error log:
>> 
>> /cgi-bin/STORE/process.html Unable to send mail using /usr/lib/sendmail
> Have you read the sendmail error log at all?  That is probably where the
> problem is.  And, check to see if the recipients have valid addresses...
> maybe???  We're on the right track.  Let me know what happens
> 
> Brandon

I did check the mail logs and I see no errors. There is other mail 
activity around the same time but no errors.

The recipient email address is valid... it is my own. These are the 
order notifications that come to me, not the receipts emailed to the 
customer. This is odd because I never saw it until a week or so ago and 
I'vehad hundreds of normal orders. I appreciate your input.

DB