Birthday mail

I saw a [BIRTHDAY] tag with the description: It requires the birthday custom field value to be in the format of Y-m-d (i.e: 2015-07-01) in order to work properly.
But I can not find the birthday custom field.

Is it possible to send out auto birthday emails?

Thank you
The [BIRTHDAY] tag is for using inside an email the same as any other tag. You can create custom fields within any given list in the Customer area.

As far as I'm aware you can't send an email automatically on a subscribers birthday, if that has changed @twisted1919 will be able to confirm.