Yahoo sign in fail

[maddavew]

I'm new to Zimbra, for a few years I have used Yahoo.co.uk mail but about January this year I could no longer access my Yahoo mail directly via my web brouser. (Mozilla/5.0 (Windows; U; Windows NT 6.1; en-GB; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.3).
So I reluctantly started using Windows Live Mail, but over the last few days that developed a similar problem.
Finally I turned to Zimbra and that worked fine yesterday, but today I have the old problem back again:It seems like the server is not there or my sign in details are wrong, but that is not so, I've used this email account for years, also I have never lost access through my smart phone during any of this. Any suggestions?