Mail offline all day

OK - so from time to time Mail decides it does not want to play anymore and goes offline. This however is usually for a relatively brief period and then it rights itself. Not so today and I am getting frantic!
Here are the facts:
OS 10.6.8
Tried to take accounts online via the menu bar - no luck it just flicks at me.
All settings under mail preferences are correct. Nothing has been changed and they all worked yesterday.
Closed and opened Mail, rebooted the computer, checked for updates, deleted and re-added the account (tried it with one only) still absolutely nothing. It has never been off for this long before. Starting to twitch as I work from home and I need to be able to access my mail in a hurry.
Connection doctor says it can access the internet but not the servers. Again - all settings are correct as far as I know (I not only have not touched anything but compared the settings with my daughter's account on her laptop just to verify - AOK) PLEASE if there are any other ideas or suggestions PLEASE advise. I will of course have to keep checking my mail now for any response via Google - Auuuugh!
Thanks

This happens to me infrequently and is usually a problem with my internet service provider. You might give them a call before you change a setting on your computer like I did once.

Have little to add to this one other than to let you know that mine is pulling from my @me and @gmail accounts all day. I'm thinking that this is an ISP issue.

It took two days and then it righted itself. It has never taken this long before. If it were the ISP then surely everything would be affected? Everything else is perfect - as mentioned I can access my mail - receive and send after accessing my accounts through Google, so I will just accept that it is a quirk with the Mail app that apparently there is no cure for. (Have spoken to others who experience the same issue) I will just have wait it out every time it happens. Still mightily frustrating though...
TTFN and thanks for the comments.