rewrite sender email address

[alexm2017]

Dear admins,

I have the following situation to solve:
When an employee is sending an email using outlook with his account ex: user1@domain1.com, the server should rewrite his address with alias user1@domain2.com.
I know there are some possibilities with "Send AS" and "Send on behalf" but is not working... i mean from outlook i need to create a new Identity with alias user1@domain2.com.
But i cannot reconfigure outlook (too many users) so i need to make a change in the server that doesn't need changes on outlook.

Also as a bonus: there is a way to rewrite the sender ip adddress only when the sender it is sending to gmail.com domain?

Thank you