iTouch and @live.com email account not sending

Hi. I've set my son up with an iTouch and @live.com email account.

It was working fine when I chose 'other' in the 'add account' part of settings a week or so ago.

Then, a couple of days ago it stopped sending emails.

I searched on these pages and it suggested I change the port to 587, rather than the 995 it had defaulted to.

Didn't work.

So tonight I deleted the account; redid it as 'Microsoft Hotmail' in the 'add account' part of setting (as recommended by Apple) and it still isn't working.

It received an email but still can't send saying 'cannot send mail: an error occurred while delivering this message'.

Does anyone know why? I've never had this problem with the different email accounts I have on my iPhone 4....!

Thanks.