Having just had 4 emails to my sister in the US returned undelivered, I contacted Tiscali to find out what the problem is. The response is that subsequent to last years spam and virus issues sent via Homechoice/Tiscali servers, many US networks now have the Tiscali servers blocked. Yet another reason why Tiscali becomes less and less viable as a service. As an Apple user with very good firewall and virus protection systems in place I was also dismayed to hear that they no longer support Apple products. Maybe Virgin Media can offer a better service as Tiscali looks like its circling the drain.

Hmm....I send a few emails to the States, never had a problem or any returned undelivered...

I think its just emails that contain attachments or links.

it's more likely the us server that is blocking the emails if theri is a contact address in the bounce back try contacting them or gert your sister to contact them to request the block be removed. or if you are sending attachments perhaps they exceed the size limits that they will accept for emails

Tell her to sign up to a web mail account,problem solved.