Windows Live mail appears to have sent my out going mails but they are not arriving at their destination.

Hi there Since yesterday the emails that I have been sending are not being received by my clients. They appear to have gone as they land up in my sent items folder but nobody is getting them including the test mails I am sending myself. I am receiving emails. My service provider says everything is fine on their side and my website host cannot find any problems on their side. I have checked mail set up and all is as it was. My business partner and myself have 6 email addresses that we use and we operate on seperate laptops yet neither of our out going emails are getting to our clients 

I am running windows 7