How to get JIRA to send an email to the assignee ?

[Shanti Subramanyam]

I've created a bunch of issues and assigned them to Sheetal, Akara etc. 
However, they do not know that these issues are assigned to them as they 
don't receive any email. I looked around but can't seem to find any 
setting to tell jira to automatically send an email to the assignee. 
Even as the user who creates the issue doesn't get any email unless I 
specifically 'watch it'. I can watch issues I create, but how can I 
watch an issue if it has been assigned to me but I have no idea about it ?

Appreciate any help
Shanti