This isn't an error this is an Advise message
the bounce back is advising you that you are sending too many messages so breaking the message Limits of the service
the ammount of mails being recivined isn't the problem here,
The issue is the ammount the individuel is trying to send through BTinternet.com the "Residential" Service (i get this from your Other Forum post with teh server being mx.bt.lon5.cpcloud.co.uk # #SMTP#)
so my guess from your post, is that you are speaking to someone who is trying to send a Marketting mail shot probably to several 100 people, and getting that error,
if thats what the customer wants to do then none of the BT Mail services will suit, (btconnect and btinternet) are both not designed for MaiL shots)
I would suggest you/your customer uses a Programme like Mailchip which is designed for Mass Mail Purposes