Share your experience!
I had recently bought xperia E3 and came to know that that any earphones or headfones does not fit properly in the jack.
Is this a manufacturing defect or what is it? 
For hardware issues you think you may have you are best to either return your device to the place of purchase or contact Xperia care and have it inspected http://www.sonymobile.com/global-en/support/contact-us/
@Trg - I would advise first cleaing the heaphone jack gently with something soft like a cotton tip to rule out anything in the jack that could be causing the issue.
I had the same issue right off the box.
Had to force it a little bit to enter fully. Now it's normal, fits entirely in.