There are any reasons for not being able to connect to your email server, including:
Unfortunately, the combined effect of complex personal anti-virus/firewall software and non-expert computer users inevitably leads to situations where people manage to lock themselves out of the internet without any help from hackers! Crazy but true. One of the first things to try if you find you can't connect to mail or websites, is to temporarily disable your firewall software. This will remove any blockage between your mail/web browser program and the internet connection that comes into your home/office. If you find that you can then connect to websites/mail as normal, then you need to remove some of the rules that have been configured in your firewall software.
Almost every internet connection requires a "Port" number in order to work. Servers have thousands of virtual "Ports". Think of a Port as nothing more than a numbered doorway into the server "building". It is convention that SMTP connections are made via Port 25. Some ISPs, (including BT Internet and others) prevent outbound connections on Port 25 to anything other than their own mail servers. This is a growing practice (already standard practice in the US). In order to circumvent this, you can connect to our SMTP servers via Port 525. Or, if you want to use a secure SSL connection, you can use Port 465 or 587.
Once you disable your firewall, and find that you are still unable to connect, then you should check your broadband router to make sure it is showing the correct indication lights. Sometimes, the classic "switching it off, waiting a minute, then turning it back on again" may fix the issue. You may need to call your ISP support helpdesk to confirm this.
It is amazing how often mail connectivity problems are caused by something as simple as a seplling error (oops!). Make sure that you are using the correct SMTP and POP3 server names, and that your POP3 login name and password are typed in correctly (sometimes, an O 'oh' might appear to be a 0 'zero' for instance). You might be requested to enter a password or see an error similar to "There was a problem logging onto your mail server. Your password was rejected." This is certainly due to - you guessed it - having the wrong password configured!
Your computer has to connect to our server in order to fetch your new messages. This obviously places a load on the server (when you consider we deal with many hundreds of requests every minute). Therefore, when you configure your email client, we suggest a minimum time of 5 minutes between automatic send/receive's. If you connect more than 60 times in an hour you may automatically be prevented from connecting for the next 60 minutes. This is to protect the quality of service for everyone else.