1. Am I allowed to use automated mail program (written by me) to send emails(using my email account) to those users who register with my service? If yes, what strategy should I follow so that my account is not blocked? Is there any provision of white-listing of the IP address from where the email originates?
2. If the answer to the above question is "no", then what approach should I follow?

FYI, I am building a useful service (and not some unsolicited service or spamming ) that would use automated email sending script to do the following:
1. The activation code to the user that register with this service.
2. The new reset-password, in case the user forgets his/her password and he/she requests for the same.