SMTP-receive connector

Hi, i have registered my domain in godaddy.com, domain name is domainname.com and my mx record is mail.domainname.com and priority 10 and have only one mx record. I have created mx record and a record in my local dns server
DNS RECORD DETAILS ( IP ADDRESS OF LOCAL DNS SERVER 192.168.1.150)
Host and child domain : mail
FQDM:                  domainname.com
FQDM of mail server:       mail.domainname.com
PRIORITY:            10
Then I created A record
 NAME:                  mail
 FQDM:                  mail.domainname.com
 IP Address:            192.168.1.151 (my exchange server ip address)

PORT FORWARDING DETAILS:

External port            25
Internal port             25
Protocol             both
To ip address            192.168.1.151 (Exchange server ip address)

EXCHANGER SERVER DETAILS
Accepted domain: domainname.com
Send connector: Smart host
Received connector:  default

It seems everything is perfect about my configuration to send and received the mail from outside. Now my problem is I can able to send email to outside, but I can’t receive email from outside.