Thanks to everyone for their help and in particular Carlton. We created a A-record for "mail2.tridentgarages.com" for 213.2.206.202 and changed the PTR record for 213.2.206.202 to be "mail2.tridentgarages.com". A couple of hours later all the queued mail for Barclays had been sent. Probably not a coincidence! Cheers. Chris.