Could Not Find Stored Procedure 'xp_sendmail'

I created a trigger in the pubs database:

create trigger test3
on authors
after update
as
exec master.dbo.xp_sendmail "joebob@yahoo.com","Hello"

I then run this script in QA:

update authors
set state = 'CA'
where state = 'KS'

and receive this error message:
Could not find stored procedure 'xp_sendmail'.
The statement has been terminated.

What do I need to do ? I realize that xp_sendmail is in the master database, but want a trigger fired to joebob@yahoo.com anytime an update script is run against the authors table in the pubs database.
I've set all the executable rights....what else do I need to do ?

Thank you