E-mail is probably the best way!
However if you have a front end, back End arrangement then it is possible to have the messages stored in a message table on the back end, and then on the front end database have a hidden form that uses the timer event to interrogate this database periodically to see if there are any new messages. If there are, it pop's up another form showing the message.
I have seen this done, I don't recommend it, it's a bit messy, and it's best to avoid the timeer function within your database.