Adjust this one-liner to use your internal mail server and Gmail and add it to Gaia's job scheduler:
grep -e "HTTP login denied\|Web UI connection.*was a failure$" /var/log/messages* | grep -vxFf /usr/tmp/sent 2>/dev/null > /usr/tmp/new; [ -s /usr/tmp/new ] && cat /usr/tmp/new >> /usr/tmp/sent && { sleep 2; echo -e "EHLO $(hostname)\r"; sleep 2; echo -e "MAIL FROM:<fw@$(hostname)>\r"; sleep 2; echo -e "RCPT TO:<you@gmail.com>\r"; sleep 2; echo -e "DATA\r"; sleep 2; echo -e "Subject: [$(hostname)] Login failure\r\n\r"; cat /usr/tmp/new; echo -e "\r\n.\r"; sleep 2; echo -e "QUIT\r"; } | nc -w 30 smtp.gmail.com 25