Live mail msgs being showing as ‘sent’ are not received

This is a Live Mail question.  I have an intermittent problem with mail that I send not being received.  The mail msg leaves the outbox but is delayed in being received.  I have been blind copying myself to see when this happens, but it doesn't seem to have any pattern to it.  My incoming mail always seems to get to me, regardless of the recipients.  Only the outgoing mail is having problems.  My email provider that I use/link to in Live Mail is Earthlink.  Any suggestions as to what I can do?  I have had Live Mail since Nov 2011.  This started happening about 2 months ago.  Prior to that I hadn't had any problems.