Yep, same problem here. Everything was working up until last Monday or Tuesday. I can GET my mail but I cannot SEND ANY mail, even on my web mail now. Tried setting up new POP3 profile, failed, tried setting up new IMAP profile, failed. Had phone support tell me it was a block due to suspicious activity and the live chat gave me que card solutions that didn't work and told me that I had been moved to Yahoo mail. Went there and they didn't know of such an email address. Also got a voice mail from a Cox rep telling me it was a known issue and that it had been resolved. It hasn't, still can't send email in desktop Outlook or my webmail.
This transition is truly a terrible mess