I am looking to send out emails to users in my WordPress site/system. I want to have emails that say something like:

You have X credits remaining to fulfill Y.

Your deadline is Z.

X,Y,Z would be information pulled from custom fields i have created in the system and/or from sql queries.

I am looking for either a plugin or some tips as to how to go about doing this manually through code. I will be sending these out on demand as well as monthly, etc.

Thank you for your guidance, and let me know if you could use more information. I tried to keep it as simple as possible. Maybe wp-mail is the way to go?