SSMTP is a email service for Raspbian and is used for sending out emails internally in a network and externally.Its a very simple install and will get you up and running in no time. This process would need a Root account and make sure you update Raspbian to the latest patch level. You can update by running "sudo apt-get update".
First Install ssmtp package via apt
# apt-get install ssmtp
# apt-get install mailutils
Now edit the ssmtp config file.
Add these lines in it for external mail server
AuthUserfirstname.lastname@example.org AuthPass=password FromLineOverride=YES mailhub=smtp.gmail.com:587 UseSTARTTLS=YES
That's it all done. Now try sending a Test email.
# echo "Test Mail" | mail -s "Test Email" email@example.com
If you encounter any errors during the process, let us know via Contact Us and will get it resolved promptly.