I'm a Barclays customer, so I've just taken a look at the full headers for genuine emails sent from Barclays. They all show 'assure1.barclays.co.uk' as the sending server, with an IP address of 176.74.179.99
Examine the full headers for one of the emails you've been receiving to see if that's what you also see. (To view the full headers you might need to click on a little 'information' button or just look for something like 'view extended header'). If you see something similar, the emails are genuine; if you don't, they're fakes.