[Exim] acl_check_rcpt

Hi List.

Wonder is someone can assist with this acl condition.
I am struggling a bit with regex's.

We are getting alot of mail to user & numbers in the localpart.
This is an invalid format for our servers.
No accounts end in numbers.

i was thinking of adding a condition like the 1 below to the acl_check_rcpt:

deny    message    = Invalid username. Please stop sending to it.
        condition  = ${if match
{$local_part}{\N$local_part{6}[A-z0-9]{6}\N}{yes}{no}}
           domains = domain.name : domain1.name

the format is incorrect and I cant seem to get it right.

Below are examples to the address they are sending to:

cg8da6qz6@???
rollo192@???
npaaha5447d2q@???


Thanks in advance

Regards,
Tom Kinghorn