list index out of range

[vinay-vik]

I have written a code to generate mails for multiple recipients using the following code.

sendGridEmail = SendGridEmailMultiAlternatives(subject,message,from_email,recipient_list)
sendGridEmail.attach_alternative(mail_content, "text/html")
sendGridEmail.sendgrid_headers.addTo(to_send_email_list)
sendGridEmail.sendgrid_headers.addSubVal('%investor%', name_list)
sendGridEmail.update_headers()
response = sendGridEmail.send()

where recipient_list is empty and I want to update recipient_list using sendgrid_headers.addTo(to_send_email_list). I am not able to send mail because of empty list(recipient_list). Is there any way to update sendgrid_headers.addTo and send mails.

Thanks