He has not been able to access this account for a couple of months.
What do mean by unable to access? Unable to login? Able to login but cannot see anything? ...
Your error message relates to sending an email. Are you doing this from a mail client on your PC, like Outlook, or as webmail? Fsmail a/c's are webmail only.
Later you say nothing can be seen but items can be deleted. What items if you can't see any part of the account?
FSmail is a free webmail only account which are available to anyone not just Orange customers.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC