new to BTinfinity.. got my btinternet password;

I can log in to btyahoo and if I send an e-mail to my Hotmail account it gets through.

If I try to send an e-mail from my btinternet email account from Outlook2010 in Windows 7, it gets sent but never arrives in my Hotmail (or my friends' hotmail) accounts.

Worrying because it makes me wonder what other e-mails I might send but never get through with no rejection message!

Oh.. and I can sent an e-maiul to my btinternet address FROM Hotmail; no problem, gets through to my Outlook 2010 on my desktop, no worries and yes the btinternat address IS in my safe senders list in Hotmail..

Any ideas?

Original title: hotmail received from BTyahoo but not from btinternet from Outlook