Do you know any way to send periodical emails automatically?

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I have been searching this for a while and wasn't succesful. I've got some books from my college library. And it should be renewed once in two weeks. It can be done by sending an email to our library with the book codes. I have created a reminder for making me remember about it at the correct time. But if there is no internet connection at the time of reminder then I will probably forget about the whole renewal thing and it happened again this week. I've got to pay a fine for this days which I forget to renew the books. I once had an app in my phone which automatically send these emails every two week. That was really helpful. But now it asks me to pay for it which is more than the fine I had to pay. So that make no sense on using it by paying. So I need some help finding any free service or app which sends an email periodically? And if it works without internet, means if it is an online service then I've got just the thing. Do you know anything like this?