[Exim] host_accept

Hi ,

I am unable to understand as to how should i give the option

host_accept_relay =

(ecom.com is my domainname and mail.ecom.com is my mailserver gateway
running exim 3.16
D1.ecom.com, D2.ecom.com,D3.ecom.com are subdomains )

I want users from ecom.com and ( D1-D5 ).ecom.com to relay mails rest no
one
should be able to relay mail outwards .should my options be

host_accept_relay =*.ecom.com
or
host_accept_relay =D1.ecom.com:D2.ecom.com:D3.ecom.com:

SECONDLY

mail.ecom.com is my mail server gateway .I have my DNS server also
configured over here ...

An entry in the MX records would be fine in my dns server to exchange mails
.or some other setting has to be added in configure file ....

Regards
Raj