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
Final Solution:
#! /bin/bash
# looks at date of cert expiry on cmd line
#
uExpire=`/usr/bin/curl $1 -vkI --stderr - | /bin/grep "expire date" | /usr/bin/cut -b 17-`
dExpire=$(date -d "$uExpire" +%s)
dNow=$(date -d "now + 3 weeks" +%s)
sExpiry=$(( (dExpire - dNow) ))
if [ $sExpiry -lt 0 ]
then
echo "Cert will expire in less than 3 weeks"
echo "something wrong with renewal on $1"
fi