There are some common threads in this forum about similar issues where folks are unable to send email. In my case, this started on the weekend of 14-Sep-2013, and I didn't notice it until today. It turns out that GoDaddy changed some of their security settings, and you can no longer connect via localhost to their mail servers.
A similar post in this forum mentioned getting "Connection Refused" errors, and this was what I saw too. The post mentioned using "localhost", but that will no longer work with GoDaddy. You need to directly connect to their relay mail server. The entry should be:
Note that you'll have to use your GoDaddy email account in the outgoing From address in order for it to work, since GoDaddy checks for valid accounts before relaying. However if you set it up this way, your outgoing mail through GoDaddy's servers should work again.
Good luck, peeps! ;-)