Emails being sent from my PC are not being received by anyone.

It shows all messages that I have sent in my SENT folder but still they are not being received by any of my contacts.  Also when I send a test message to myself they go directly into my SPAM folder.  I have been 2 weeks trying to get this resolved and the phone assistants have been no help with spending hours and days at a time since the end of July.  Any help would be greatly appreciated.