Bounce when mailbox full (but it shouldn't)

[protocol]

We have several Cpanel 10 serveral and are setting up a new Cpanel server with v11.

The exim.conf on the Cpanel v11 server seems to include:

virtual_user_maildir_overquota:
driver = redirect
condition = "${perl{checkuserquota}{$domain}{$local_part}{$mes sage_size}}"
user = "${lookup{$domain}lsearch* {/etc/userdomains}{$value}}"
domains = lsearch;/etc/userdomains
data = :fail:Mailbox quota exceeded
allow_fail

This causes mails for users with full mailboxes to bounce rather than queue.

Please note "Discard email for users who have exceeded their quota rather than keeping it in the queue" option on exim config part of whm is NOT ticked.

So why is this appearing? it is no in any of the other servers' exim.conf files.

Thanks in advance for any thoughts.