send emails on condition: import of contacts

Hello Team,

I have a list of 300 contacts say list1, and want to send set of 3emailers (day1 , day4,day7). Every 2/3 days I have a new set of contacts that need to be imported into above list1,
how do I set the trigger for import and send those sequence emails to imported contacts? Is there any way to trigger and send emails on import of contacts every time?? How do I accomplish this.

Regards
Yogesh