It's imperitive that everyone who wishes to play for the club, replies to the email they receive from the FA.
The FA run a programme called 'The Whole Game' , this is an online portal where every footballer has their details stored and are visible to clubs they may play for.
Every player has a FAN (FA Number), with which they can login to the FA website and edit their own personal details (a change of address, mobile number or email). These will need to be kept upto date.