Hello and welcome to the forum. Normally you would ask a tech question in one of the specific forums.
To do "automatic" anything in Access, remember that if you don't launch it, it ain't there. So try posting in the General section with a more thorough explanation of the requirement, focusing on exactly how often these reminders need to be sent. For the actual transmission, it should be very easy to send messages any of several ways, but it would help if you could specify which mail utility you are looking to use. E.g. Outlook, GMail, something else...?
By the way, don't be put off by me saying this is the wrong place to post. Happens almost every day. We are forgiving, but the key is to know that not everyone looks at introductions. Our problem solvers DO look in the tech topics, though.