Just disabling Norton may not work as the default Firewall then takes over.

Restart computer in 'Safe Mode with Networking' mode to completely disabled the computer and installed Anti-Virus product. Check if it works now. If yes, this means it's likely your Anti-Virus and/or Firewall controlled by Norton is blocking the port. You are in luck because I'm also using Norton 360, so I can tell you where to look.

It is possible that Norton got confused by the Thunderbird update and thinks it is a different program or one part has not got set up correctly so a port is being blocked. Try this first.

• Exit Thunderbird - this is necessary.
• Start computer as normal.
• Access Norton
• Under 'Settings' > 'Firewall' > 'Program Control'
• scroll down until you locate C:\Program Files (x86)\Mozilla Thunderbird\thunderbird.exe

It should say 'Allow', but select 'Custom' from drop down option. A new window opens: Does it say exactly the following: * Thunderbird, Allow, Direction: In/Out. computer: Any, Communication: Any Protocol: All And is the checkbox selected with a blue X ?

If no, something is different from the above, eg: Any Protocol does not say 'All'

• click on 'Modify'
• Actions tab - select 'Allow
• Connections tab - select last one -'Connections to and from other computers'
• Computers tab - Select 'Any computer'
• Communications tab - select 'All'
• Advanced tab - select If explicity requested
• Description tab - Type Thunderbird
• click on all the OK's
• Then make sure it says 'Allow'

If it says all of that already: See if the following forces a resync - select 'Block' and click on Apply and then cick on 'Close' and exit Norton.

Then access Norton Firewall again, look for Thunderbird as before and select 'Allow', 'Apply' and 'Close'

Now start Thunderbird.

Many thanks for your very comprehensive and thoughtful reply - it never fails to amaze me how some people selflessly spend time and effort helping strangers. It is greatly appreciated.

Prior to getting your reply, I had tried removing the password for the POP3 account to try to establish whether it got that far or not. Needless to say it made no difference (or at least it didn't ask for the password before "timing out".

When I got your instructions, I tried to get in to Safe Mode with Networking and although I thought I had done it correctly (option 5 seemed to say exactly that). It looked like I had no Network connection. Consequently it just failed to reach the server.

However, when I restarted in my normal mode and opened Thunderbird, it looked for the emails and asked for the password and then proceeded to download the emails that were on the server! I've gone out and back in again and left it for a while but so far it is still downloading again correctly.

So I've not had to look at or change any settings in Norton at the moment but will retain your instruction in case of a return of the problem.

Once again though I'd like to thank Toad-Hall for your time and "being there".