mail with attachment

[#1]

I receive this message when i try sending email with an attachment.
An error occurred while sending mail. The mail server responded:  tNC81n0070qPtZB01NC9R0 message rejected due to spam or virus. If you believe this is in error please login to your portal or contact your ISP support team.. Please check the message and try again.
first sent it with 3 attachments total 5mb
then tried with just 1.2 mb and got same answer from a bt address then tried a different none bt with same result
not had any problems before

[#2]

seams to be working today sent the same email to 6 people on different networks and had no problems