Whether TalkTalk care to admit it or not, it's a problem with their email server.
As email is passed from one server to another, the receiving server sends back a 'receipt' (in effect saying 'Thanks, I've got that'). If the sending server doesn't get a receipt it assumes that there's been a fault with transmission and re-sends the mail. If it still doesn't get a receipt, it again sends the mail and waits for a receipt. If it doesn't get that receipt . . . . Oh, I'm sure you've got the picture by now!
That process continues until the sending server reaches a pre-set limit and gives up trying. At that point it's likely that it will send a 'bounced mail' message back to the sender.
So, if TalkTalk's server isn't issuing receipts for incoming mail, you'll get however many copies the sending server was set to try (which is often 50 but can be 200, or even 2000), while the person sending it will get a message saying that it was undeliverable!
Hassle TalkTalk!
(Or simply get a decent email account:
http://www.gmx.co.uk/ )