Microsoft has clearly been the forerunner of a lot of Internet-related activities including the Outlook Express. But wherever Microsoft goes, a string of errors follow – this is true even for Outlook. As you probably would have predicted, there are a plethora of errors in this mail application, and since it’s hard to discuss them all, we’ll just look at a few important ones that have haunted most people. 
In some sessions, the authentication does not load properly and therefore your account configuration fails. Usually, closing and restarting Outlook Express helps in this case. If it still does not help, it would be wise to reset your account before trying to load Outlook Express again.
On rare occasions, you might even have to reinstall Microsoft Outlook again. There is always the common error which strikes periodically for the certificate – Invalid Certificate content and date error.
In this case, all you can do is to wait while your certificate gets reissued by your authority server. Microsoft is good with finding out if your account is being used in two different places at once. If you get this error – User already connected, you can understand that you are already logged in to your account from another machine or connected directly to the server through a browser.
Close the existing sessions and wait for some time before trying to login to the system again. If that does not work, your account may be blocked or locked or even compromised.
It is better to check if you are connected to the Internet before opening Outlook to avoid the application throw out errors saying “you’re not connected to the server”.
If you can still open web pages on your browser but cannot log into your mail account through Outlook, it could be because you have configured your mail server wrong or maybe a Firewall application is blocking connections to the mail application.
In this case, you can restart your computer and try again. If it still does not work, you have to get an expert to check DNS numbers and reinstall the TCP/IP connections.
There are some known issues with the message download completion in which case the pop3uidl file might be corrupted. Deleting this file and reconnecting works most times. If you receive this error – “cannot find host”, it means that you are either not connected to the Internet or your configuration file is corrupt or maybe you did not specify the correct mail server configuration.
