Broadband, mails and blocking of mails

I have my broadband connection with TDC and have had comparatively few problems – until this week when I suddenly could receive mails, but not send any.
I have a mailbox with TDC – that works, but the mailbox that is linked to my home pages etc. refused to allow me to send mails. So I contacted my webhost and asked them to fix the problem.
They explained that it was TDC that had somehow put my address on a spam filter and that I would have to contact TDC to get off the ’black list’.
So I called TDC, who told me (very patiently) that they do not support Outlook, but that there is a detailed set of instructions on how to fix the problem on the TDC homepage.
When I asked why I had been put on the blocked list he said that it was something that TDC had set up a couple of years ago and it was just chance that I had not been inconvenienced earlier.
Well, I think it is outrageous that –
 1. They treat their customers like that, and
2. That I had not been informed by TDC that this system had been set up and warning us that problems are very likely.
I have not tried to sort out resetting the mailbox – I know it’ll take much longer than expected ….