You have set up the same e amil account on each users account.
To stop what is occuring you will need to delete this account from all but your settings.
With Blueyonder you can set up up to five seperate accounts for each real e amil address. Go to theri help pages for an expanation.
I have three clone accounts linked to my real account. This gives each person an individual e mail address and this can be set up in each of their own user profiles