Every object has three qualifiers: server, database and owner. You can call any extended stored procedure from any database using the following syntax:
EXECUTE master.dbo.xp_sendmail
OR
EXECUTE master..xp_sendmail
Both if this lines will perform the same. In the second one, I've omitted the owner but left the qualifier delimiters. This is a shortcut and means the same as
dbo.
-Mike