how to send bulk email in Codeigniter ?

[eluser]depthcharge[/eluser]
Here is how I would basically go about it.

1. Create a queue system in the database (tailored to your specific sending requirements)
2. Enter emails within this queue
3. Cron job periodically checking the queue, pulling ** amount from queue and sending (allowing rate to be modified for tweaking).
4. Handle Bounces using some kind of VERP system.

Codeigniter's email class has good documentation within the userguide for sending the emails.