Hi paul,

Thank you for your question.

Yes, we could block single user or multiple user  to communicate with external domain by the transport rule as the following command:

New-TransportRule -Name 'block communicate with external' -Priority '0' -SentToScope 'NotInOrganization' -FromScope 'NotInOrganization' -DeleteMessage $true -Enabled $true

If we want to block some domains for all internal uses, we could use the block list on Exchange edge server by the following link:

https://technet.microsoft.com/en-us/library/bb124701(v=exchg.150).aspx

If there are any questions regarding this issue, please be free to let me know. 

Best Regard,

Jim

Hi ,

Thank you for your question.

We could refer to refer to the  following steps to create transport rule:

1.        Login  EAC
2.        Navigate to  mail flow->rules->+
3.        Create a transport rule as the following snapshot:

If there are any questions regarding this issue, please be free to let me know.

Best Regard,

Jim

Thank you so much ,now its totally clear for me. but one thing jim like if i need to block number users so i can create many rules or i can create DL and put them user's inside the DL...?

Hi Jim,can you please help me for this 

in my environment i have 30 distribution groups which is like a.dept,b.dept,c.dept,...etc. there is a user name "user 1" need to add all this groups on single shot

Thank you so much ,now its totally clear for me. but one thing jim like if i need to block number users so i can create many rules or i can create DL and put them user's inside the DL...?