Hello experts,

I've Recently installed ZCS 6.0.13 on ubuntu 10.04
now problem is I can send/receive mail withing the my domain but i can't send external mail, but I can receiving external mails..

I got this error mail with subject "Undelivered Mail Returned to Sender"
Code:
This is the mail system at host mail.mydomain.in.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

: mail for xxxxxx.com loops back to
    myself
here is my /etc/hosts:
Code:
127.0.0.1       localhost
192.168.254.21  mail.mydomain.in mail
here is my /etc/resolv.conf
Code:
search mail.mydomain.in
nameserver 202.138.96.2
nameserver 202.54.9.1
here is my dig my.domain mx
Code:
QUESTION SECTION:
;mydomain.in.	 IN	MX

;; ANSWER SECTION:
mydomain.in.	 74112	IN	MX	10 mail.mydomain.in.

;; AUTHORITY SECTION:
mydomain.in.	 71415	IN	NS	ns.mydomain.in.

;; ADDITIONAL SECTION:
mail.mydomain.in.	71415	IN	A	180.179.36.65
ns.mydomain.in.	71415	IN	A	180.211.98.131
here is my dig my.domain any
Code:
;; QUESTION SECTION:
;mydomain.in.			IN	ANY

;; ANSWER SECTION:
mydoamin.in.		74695	IN	A	180.211.98.131
mydomain.in.		74089	IN	MX	10 mail.mydomain.in.
mydomain.in.		71392	IN	NS	ns.mydomain.in.

;; AUTHORITY SECTION:
mydomain.in.		71392	IN	NS	ns.mydomain.in.

;; ADDITIONAL SECTION:
mail.mydomain.in.	71392	IN	A	180.179.36.65
ns.mydomain.in.	71392	IN	A	180.211.98.131
here is my hostname
Code:
mail.mydomain.in