Been using letsencrypt for a while now, and they have announced that they will no longer send expiry emails out. Need to find a solution to test the certificates to see if they are almost expiring. This looks promising: https://nickjanetakis.com/blog/using-curl-to-check-an-ssl-certificate-expiration-date-and-details
Now need to compare the date to current date and send email as appropriate. This is close: https://unix.stackexchange.com/questions/24626/quickly-calculate-date-differences