How do I edit the "message" that's displayed on the "edit post" screen?

I’m working on a plugin that hooks an action into the publish/update button on the edit post page.

I have this part working, but I’d like to also update the user as to what was done. How do I add to the list of messages that can appear on the edit_post page?

In other words, I’d like to say “Post Updated. An email was sent to XXX” instead of just “Post Updated”.

Thanks,

Anca.