It's hard to track why your computer crashed and restarted, but you can e-mail your logs with the notification e-mail. For advanced monitoring, I suggest trying out Zabbix, NagiOS or Cacti.
However, here's a simple Python 2.7 script for sending an e-mail with a command "./script.py username_for_gmail path_to_letter":
args = getopt.getopt(sys.argv[1:], ":")
laiskas = args
SENDER = "no-reply@" + args
mssg = open(laiskas, 'r').read()
RECIPIENTS = ['email@example.com']
server = smtplib.SMTP('smtp.gmail.com',587)
server.login(args + "@gmail.com","R7olM6Qw")
You have to change R7olM6Qw to your own GMail password. Also, please change RECIPIENTS variable for your addresses. The script needs smtplib and python2.7, which may have to be installed on your server from apt.
Then you can create a simple text file next to the script:
Subject: Computer powered on!
Random text here...
In the end, just add a new line to the /etc/rc.local file:
/path/to/the/python/script gmail_username /path/to/the/letter
However, this is not a safe method as you will be storing your password insecurely, so I suggest creating a mailbox just for that. Also, please, mind it and chmod all scripts in order to prevent other users doing anything with them.
Instead, I think that it is rather more reasonable to have a separate server with PHP mailer script available only for servers' IPs. In that case, the separate server would be doing the mailing service securely, while leaving your other servers only with curl or wget for pushing the notifications.