I had a problem whereby e-mails from my brother would not always arrive at my work e-mail account. After protracted investigation the cause was found to be a specific combination of anti-spam rules not at my employer's gateway to the big wide world but their ISP's entry point. The ISP at the time (Not Telia but one of the other bigger ones in Sweden that I can't recall now) made some changes and there have been no problems since. Interestingly one of the several anti-spam rules comprising the cocktail in question involved blocking e-mail from that tiny UK domain called btinternet.com!
