Since adding another user account yesterday to my Windows 7 HP desktop, any mail I try to send ( from either account ) brings up a Norton dialogue saying" 554 transaction failed due to possible abuse" and takes me to postmaster.yahoo.com/abuse_smtp.html
No incoming emails are affected.
If I send the same message from Windows live mail or log into BTYahoo mail, the message sends without problem.
Is it Thunderbird or Norton?? Would welcome any assistance