[exim] deny relying if sender is not in a domain

Hi.
I have been looking for a way to allow delivery of a mail
but only if sender is in my domain.
I´d like to restrict the mail addresses that my users can use in my lan and
have a log of those mails sent.

They should only send from addresses in @grupor.com.mx
MAIL FOM: user@???
if domain part is not grupor.com.mx a 5xx should be issued.
I noticed that there is no acl_smtp_mail to check with.
How can I do this?
BTw, I am forcing them to use my exim by doing a iptables -p tcp --dport
25 -j redirect --to 25.

Thanks in advance.
Sebastian Muñiz.