If I tell you the problem I have which occurrs about once a month. Perhaps what I do to resolve it may help you. I have been onto the BT help line 50p a minute scary I know, but they were as much help as a chocolate tea pot.
Every now and then when I try to access mail I get the error message; failed to connect server etc etc.
When the problem occurrs I go to Outlook Express, Tools, Accounts, All - and highlight the mail default account. Then click Properties, Servers... the incoming and out going mail in 'mine' should read the same.
i.e. mail.btopenworld.com. The top one is blank. So I copy and paste.
Also below where is says account name this is exactly what it should say. Mine has '\mail.btopenworld.com' in front of my account name. This I delete leaving account name and click apply.
I hope this helps..Lap..