Local relay email server to manipulate email headers

Years ago I used to use a very nifty Windows software (now abandonware) that allowed you to manipulate email headers for both incoming and outgoing emails.
Once set up it worked in the background and required little or no user interaction.
Basically, it acted as a local email relay server, simple but very useful. It was meant to work with any email client.
Here is the link to the original software with the description:
http://www.xrayapp.com/xray/

Is there anything similar for Linux?
Being simple and lightweight is a major requirement, the more the better.

Thanks for your time,

Grabby