Hello Akash - the following article may help:
Question:
How do I allow outgoing relay for one recipient domain only?
Context:
How do I allow outgoing relay for one or few recipient domain(s) only?
Symptoms:
What is "not" working?
Solution:
Relaying will allow for any ip address that is on the relay list to be able to relay to any domains.
So if you need to allow only one recipient domain like example.com to be able to relay out then you will need to adjust the 'Outgoing Mail Policies', under 'Mail Policies'.
1. create a new outgoing mail policy.
2. Under add users, specify "recipient", then proceed to add the email address of the recipient domain(s)
i.e. @cisco.com @gmail.com, @hotmail.com
3. create a content filter in the new mail policy that will deliver the message with no conditions.
4. the default policy will need to be changed so that it will drop all other messages. You will need to create another content filter called drop and apply it to the default mail policy.
These steps will ensure that only message going to the recipient domain(s) will be delivered. All others will be dropped.
Remember the Outgoing Mail Policies only apply to private listeners. So if you have not created an outgoing private listener, then do so.
Please let us know if you have any questions and/or require further assistance.
Thank you for contacting Cisco Email Security.
