send notification email to user in another group
When you have a group, you can search users via the IdentityAPI.
Use a IdentityAPI.getUsersInGroup( ... ) to get the list of user in a group
Then, for each user, use IdentityAPI.getUserContactData() to get the email
Finally, using an "email connector" you send a email to a user
What do you mean by "how user receives this message in his process?" ? A user received an email in his mailbox?