Security cerificate?

I've been getting a strange pop-up lately when I try to open Windows Mail. The top of the box says "WinMail.exe" The text inside reads:

The server you are connected to is using a security certificate that could not be verified. A required certificate is not within its validity period when verifying against the current system clock or the timestamp in the signed file. Do you want to continue using this server?

There are buttons for Yes and No. At the bottom is a link that says "Get help from communities"

If I click outside of the box, it goes away but the email doesn't work. If I click "Yes", it works, but I suspect that's why my computer wouldn't start normally the next day. Even after System Restore it still pops up.

It doesn't show up every time, but more often than not. Virus scans (AVG and Windows Defender) don't find anything, but it sure seems suspicious to me because of the stilted English and because this has never come up before.

I installed Windows Live Mail, but the same thing happened, although the title was different and it didn't include the link.

Is this by any chance a valid warning? If not, how can I get rid of it?

Thanks for your help.

Perhaps I should have mentioned that my provider is ATT U-Verse and that I am able to view my mail from the ATT Yahoo page if I have to.

To troubleshoot this problem I need to know:
The name of your outgoing (SMTP) mail server, whether it is using a port other than the standard '25', and if the SSL option is enabled. Incidentally, Windows Mail is not your "mail server", it is a mail client. Turn off the SSL option. You can do so by going to. Tools, Accounts, select that account, Properties, Advanced.

Thanks for responding. Shortly after posting, I was unable to log in for quite a while; I kept getting a page saying that the site was down for maintenance or something like that. Eventually I gave up, but I thought I'd try again today and it seems to be working.

Fortunately, the problem I was having went away a day or two after I posted, so I think I'll leave well enough alone. Thanks again for offering your help.

All you have to do is just check the POP3 server and SMTP server account settings for incoming and outgoing mail is correct for the new email server. Also check the ports are set to the correct number too. You can also take a look to this website which will give you plenty of information regarding the same issue - http://technet.microsoft.com/en-us/l.../bb310795.aspx