KISS Fail2Ban send mail action with temporisation. This allows to not beiing spammed on each bans after system (re)boot or Fail2Ban service (re)start... Rely on "gracetime" script in https://github.com/kekh/Fail2Ban-Tweaks.

sendmail-whois-lines.local

[Definition]

actionstart =

actionstop =

actionban = GRACE_CMD="/usr/bin/gracetime all 10"
            if [ "$(${GRACE_CMD})" = "NO" ]
            then
                printf %%b "Hi,\n
                The IP <ip> has just been banned by Fail2Ban after
                <failures> attempts against <name>.\n\n
                Here is more information about <ip> :\n
                `/usr/bin/whois <ip> || echo missing whois program`\n\n
                Lines containing IP:<ip> in <logpath>\n
                `grep -E <grepopts> '(^|[^0-9])<ip>([^0-9]|$)' <logpath>`\n\n
                Regards,\n
                Fail2Ban" | /usr/sbin/sendmail -f <sender> <dest>
            fi